CLASS 7 CHEMISTRY CHAPTER 2
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CLASS 7 CHEMISTRY CHAPTER 2

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@Dr. K. Viswanath

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Questions and Answers

What characterizes a desirable change?

  • It is always a physical change.
  • It produces good results. (correct)
  • It produces unfavorable results.
  • It occurs due to human intervention.

    • What type of change occurs when quick lime is dissolved in water?

  • Reversible physical change
  • Irreversible chemical change (correct)
  • Reversible chemical change
  • Irreversible physical change

    • What is the result of heating sugar in a pan?

  • It caramelizes and then chars. (correct)
  • It melts without any change.
  • It turns into steam.
  • It dissolves into syrup.

    • Which of the following statements accurately describes evaporation?

    <p>It takes place at all temperatures below the boiling point.</p> Signup and view all the answers

    What distinguishes a fast change from a slow change?

    <p>Fast changes happen in seconds or minutes.</p> Signup and view all the answers

    What happens when solid ammonium chloride is heated?

    <p>It sublimes and dissociates into gases.</p> Signup and view all the answers

    Which of these is an example of a non-periodic change?

    <p>Daily weather changes.</p> Signup and view all the answers

    Why is the change from ice to water considered a physical change?

    <p>It is temporary and reversible.</p> Signup and view all the answers

    What type of change is melting wax considered?

    <p>A physical change.</p> Signup and view all the answers

    What occurs when zinc reacts with dilute sulphuric acid?

    <p>It forms zinc sulphate and hydrogen gas.</p> Signup and view all the answers

    What does sublimation involve?

    <p>Change from solid to gas without passing through a liquid state.</p> Signup and view all the answers

    What happens during the burning of a candle?

    <p>New substances are formed.</p> Signup and view all the answers

    What happens to an iron nail kept in water for several days?

    <p>It rusts, forming a reddish-brown coating.</p> Signup and view all the answers

    Which of the following best describes a natural change?

    <p>Changes brought about by environmental factors.</p> Signup and view all the answers

    How does boiling differ from evaporation?

    <p>Boiling occurs at fixed temperatures, evaporation does not.</p> Signup and view all the answers

    When salt dissolves in water, what type of change is occurring?

    <p>Temporary physical change.</p> Signup and view all the answers

    What does the heating of iron and sulfur result in?

    <p>Formation of iron sulfide, a new product.</p> Signup and view all the answers

    What distinguishes boiling from evaporation?

    <p>Boiling occurs at a fixed temperature.</p> Signup and view all the answers

    Which of the following is an example of a man-made change?

    <p>The conversion of iron to steel</p> Signup and view all the answers

    Why is melting wax classified as a physical change?

    <p>It is a reversible change.</p> Signup and view all the answers

    What characterizes a periodic change?

    <p>Repeats at regular intervals.</p> Signup and view all the answers

    What type of change involves the growth of a tree?

    <p>Natural change</p> Signup and view all the answers

    During which change is no new substance formed?

    <p>Melting of wax</p> Signup and view all the answers

    Which of the following represents an undesirable change?

    <p>Floods caused by heavy rainfall</p> Signup and view all the answers

    What distinguishes natural changes from man-made changes?

    <p>Natural changes occur without human intervention.</p> Signup and view all the answers

    What indicates that the change from milk to curd is a chemical change?

    <p>New substances are formed.</p> Signup and view all the answers

    What is a characteristic of the sublimation of naphthalene?

    <p>It involves a state change without a liquid phase.</p> Signup and view all the answers

    Which of the following accurately describes the heating of ammonium chloride?

    <p>It results in the formation of new products.</p> Signup and view all the answers

    Why is adding sodium chloride to water classified as a physical change?

    <p>The change is temporary and reversible.</p> Signup and view all the answers

    What does the reaction between zinc and dilute sulphuric acid produce?

    <p>Zinc sulphate and hydrogen gas.</p> Signup and view all the answers

    Which feature distinguishes chemical changes from physical changes?

    <p>They alter the properties of the original material.</p> Signup and view all the answers

    What happens when ice is heated and then cooled again?

    <p>It returns to its original state.</p> Signup and view all the answers

    Which observation indicates a physical change has occurred during the dissolution of salt in water?

    <p>The salt retains its original form.</p> Signup and view all the answers

    Why is the formation of iron sulphide from iron and sulfur considered a chemical change?

    <p>It produces a new substance with different properties.</p> Signup and view all the answers

    What type of change is primarily involved when water droplets form on the outside of a glass containing ice?

    <p>Physical change because it is reversible.</p> Signup and view all the answers

    Rain bringing water to crops is a ______ change.

    <p>desirable</p> Signup and view all the answers

    The change of seasons is an example of a ______ change.

    <p>periodic</p> Signup and view all the answers

    The growth of a tree from a seed is an example of a ______ change.

    <p>slow</p> Signup and view all the answers

    The process of boiling occurs at a ______ temperature.

    <p>fixed</p> Signup and view all the answers

    Burning a candle is a permanent and ______ change.

    <p>irreversible</p> Signup and view all the answers

    When a piece of paper is burnt, it changes into ______.

    <p>ash</p> Signup and view all the answers

    Changes brought about by nature are referred to as ______ changes.

    <p>natural</p> Signup and view all the answers

    Melting of wax is considered a ______ change.

    <p>physical</p> Signup and view all the answers

    When ice cubes are kept in a glass tumbler, water droplets are seen on the outer wall of the tumbler and after some time ice cubes change into ______.

    <p>water</p> Signup and view all the answers

    When solid ammonium chloride is heated, it directly changes into ______.

    <p>vapours</p> Signup and view all the answers

    When an iron nail is kept in tap water for few days, a reddish brown coating is seen on the ______.

    <p>nail</p> Signup and view all the answers

    When a spoon of sugar is heated in a pan, it first melts and changes its colour to reddish-brown and finally it turns ______.

    <p>black</p> Signup and view all the answers

    When quick lime is dissolved in water, a large amount of ______ energy is evolved.

    <p>heat</p> Signup and view all the answers

    The bowl containing milk changes into curd, which is an example of an ______ change.

    <p>irreversible</p> Signup and view all the answers

    Sublimation of naphthalene involves change of state and no new ______ is formed.

    <p>substance</p> Signup and view all the answers

    The addition of sodium chloride to water is considered a physical change because it forms a ______ solution.

    <p>salt</p> Signup and view all the answers

    The reaction of zinc with dilute sulphuric acid produces zinc ______ and hydrogen gas.

    <p>sulphate</p> Signup and view all the answers

    Heating of iron and sulphur results in a new product called iron ______.

    <p>sulphide</p> Signup and view all the answers

    Changes which do not occur periodically are known as ______ changes.

    <p>non-periodic</p> Signup and view all the answers

    Changes that produce good results are called ______ changes.

    <p>desirable</p> Signup and view all the answers

    Evaporation takes place from the ______ of the liquid.

    <p>surface</p> Signup and view all the answers

    A change that occurs very rapidly in seconds or minutes is referred to as a ______ change.

    <p>fast</p> Signup and view all the answers

    Burning a candle is classified as a ______ change due to the formation of new substances.

    <p>chemical</p> Signup and view all the answers

    The ______ of a tree from a seed is an example of a slow change.

    <p>growth</p> Signup and view all the answers

    During boiling, evaporation occurs from all parts of the ______.

    <p>liquid</p> Signup and view all the answers

    Man-made changes are changes brought about by ______.

    <p>man</p> Signup and view all the answers

    When a lighted match stick is brought near the mouth of the test tube containing hydrogen gas, a pop sound is heard and the flame gets __________.

    <p>extinguished</p> Signup and view all the answers

    Dissociation of ammonium chloride involves formation of new __________.

    <p>products</p> Signup and view all the answers

    The process of adding sodium chloride to water is considered a __________ change.

    <p>physical</p> Signup and view all the answers

    The __________ formed by heating sugar in a pan indicates the change has occurred.

    <p>charred residue</p> Signup and view all the answers

    The __________ of ice to water and back again is considered a physical change.

    <p>transition</p> Signup and view all the answers

    When quick lime is dissolved in water, a large amount of heat energy is __________.

    <p>evolved</p> Signup and view all the answers

    The __________ of naphthalene involves a direct change from solid to gas state without becoming a liquid.

    <p>sublimation</p> Signup and view all the answers

    Heating iron and sulfur results in the formation of __________.

    <p>iron sulfide</p> Signup and view all the answers

    The reaction between zinc and dilute sulphuric acid produces zinc __________ and hydrogen gas.

    <p>sulphate</p> Signup and view all the answers

    Milk changes into curd due to the action of __________ and this change is irreversible.

    <p>bacteria</p> Signup and view all the answers

    When an iron nail is kept in tap water for a few days, it develops a reddish brown coating due to oxidation.

    <p>True</p> Signup and view all the answers

    The process of sublimation involves changing a solid directly into a liquid state.

    <p>False</p> Signup and view all the answers

    Heating sugar in a pan produces a charred substance that is still considered sugar.

    <p>False</p> Signup and view all the answers

    Addition of sodium chloride to water is a chemical change because new substances are formed.

    <p>False</p> Signup and view all the answers

    When solid ammonium chloride is heated, it dissociates into ammonia and hydrogen chloride gases.

    <p>True</p> Signup and view all the answers

    The conversion of milk into curd is a reversible process.

    <p>False</p> Signup and view all the answers

    The change of ice to water and back to ice is considered a physical change.

    <p>True</p> Signup and view all the answers

    The addition of dilute sulphuric acid to zinc produces new substances and thus is classified as a physical change.

    <p>False</p> Signup and view all the answers

    When quick lime is dissolved in water, a large amount of heat is released, indicating a chemical reaction.

    <p>True</p> Signup and view all the answers

    Evaporation takes place from the surface of the liquid at temperatures above its boiling point.

    <p>False</p> Signup and view all the answers

    Sublimation of naphthalene results in the formation of a new solid substance.

    <p>False</p> Signup and view all the answers

    Burning a candle is a permanent and reversible change.

    <p>False</p> Signup and view all the answers

    The change of seasons is a non-periodic change.

    <p>False</p> Signup and view all the answers

    Melting of wax results in the formation of a new substance.

    <p>False</p> Signup and view all the answers

    Changes caused by nature are called man-made changes.

    <p>False</p> Signup and view all the answers

    The growth of a tree from a seed is considered a fast change.

    <p>False</p> Signup and view all the answers

    During boiling, evaporation occurs from all parts of the liquid.

    <p>True</p> Signup and view all the answers

    Changes that happen rapidly in seconds or minutes are called slow changes.

    <p>False</p> Signup and view all the answers

    The process of evaporation occurs at a fixed temperature.

    <p>False</p> Signup and view all the answers

    A change that occurs rapidly in seconds or minutes is classified as a fast change.

    <p>True</p> Signup and view all the answers

    Melting wax involves a permanent and irreversible change.

    <p>False</p> Signup and view all the answers

    Burning a candle produces new substances, making it a chemical change.

    <p>True</p> Signup and view all the answers

    Periodic changes are changes that occur randomly without any regular interval.

    <p>False</p> Signup and view all the answers

    Natural changes are solely the result of human intervention.

    <p>False</p> Signup and view all the answers

    The boiling point is the only condition under which evaporation can take place.

    <p>False</p> Signup and view all the answers

    Changes that do not repeat at regular intervals are classified as periodic changes.

    <p>False</p> Signup and view all the answers

    The formation of curd from milk is considered a reversible change.

    <p>False</p> Signup and view all the answers

    Sublimation is a process in which a solid directly changes into a liquid state.

    <p>False</p> Signup and view all the answers

    Heating solid ammonium chloride results in the formation of ammonia and hydrogen chloride gases.

    <p>True</p> Signup and view all the answers

    The addition of sodium chloride to water is a permanent change.

    <p>False</p> Signup and view all the answers

    When an iron nail is placed in water for several days, it develops a black coating.

    <p>False</p> Signup and view all the answers

    The change from ice to water and back to ice is a physical change.

    <p>True</p> Signup and view all the answers

    Heating sugar causes it to melt and eventually turn black due to charring.

    <p>True</p> Signup and view all the answers

    Dissociation of ammonium chloride is a physical change because no new products are formed.

    <p>False</p> Signup and view all the answers

    When quick lime dissolves in water, it absorbs heat and produces a hissing sound.

    <p>False</p> Signup and view all the answers

    The appearance of water droplets on the outside of a glass tumbler with ice is a result of condensation.

    <p>True</p> Signup and view all the answers

    What is the key difference between desirable and undesirable changes?

    <p>Desirable changes produce good results, like rain nourishing crops, while undesirable changes lead to unfavorable outcomes, like floods destroying areas.</p> Signup and view all the answers

    How does evaporation differ from boiling?

    <p>Evaporation is a slow process occurring at all temperatures below the boiling point, while boiling is a fast process happening at a fixed temperature at the boiling point.</p> Signup and view all the answers

    What characterizes a periodic change and give an example?

    <p>A periodic change occurs at regular intervals, such as the changing of seasons.</p> Signup and view all the answers

    What is meant by a slow change, and can you provide an example?

    <p>A slow change occurs gradually over an extended period, like the growth of a tree from a seed.</p> Signup and view all the answers

    What happens to wax when it is melted, and why is this a physical change?

    <p>When wax melts, it undergoes a temporary and reversible change without forming a new substance, thus classifying it as a physical change.</p> Signup and view all the answers

    In what way does burning a candle demonstrate a chemical change?

    <p>Burning a candle is a chemical change because it produces new substances, such as carbon dioxide and water vapor, which cannot revert to the original wax.</p> Signup and view all the answers

    What defines a man-made change? Give an example.

    <p>A man-made change is one initiated by human actions, such as the conversion of iron to steel.</p> Signup and view all the answers

    Why is the growth of a tree from a seed classified as a natural change?

    <p>The growth of a tree is classified as a natural change because it occurs without human intervention, driven by biological processes.</p> Signup and view all the answers

    What occurs when quick lime is dissolved in water?

    <p>A large amount of heat energy is evolved.</p> Signup and view all the answers

    Why is the formation of curd from milk considered an irreversible change?

    <p>The original substance is transformed into a new substance, curd, and it cannot revert back to milk.</p> Signup and view all the answers

    What happens when an iron nail is kept in tap water for a few days?

    <p>It develops a reddish-brown coating due to rusting.</p> Signup and view all the answers

    What indicates that the change from sugar to charred residue is a chemical change?

    <p>New substances are formed and the original sugar cannot be recovered.</p> Signup and view all the answers

    What is the result of heating ammonium chloride, and why is this a physical change?

    <p>It sublimes directly into vapors, and the change is reversible.</p> Signup and view all the answers

    What is produced when zinc reacts with dilute sulfuric acid?

    <p>Zinc sulfate and hydrogen gas are produced.</p> Signup and view all the answers

    How does the dissolution of salt in water classify as a physical change?

    <p>It is temporary and reversible, with no new substances formed.</p> Signup and view all the answers

    What occurs during sublimation of naphthalene?

    <p>Naphthalene changes from solid to gas and back to solid without forming a liquid.</p> Signup and view all the answers

    What is a characteristic of the change when ice melts into water?

    <p>It is a reversible change with no new substances formed.</p> Signup and view all the answers

    What happens when a lit matchstick is brought near hydrogen gas?

    <p>A pop sound is heard and the flame gets extinguished.</p> Signup and view all the answers

    Explain why burning a candle is considered a chemical change.

    <p>Burning a candle is a chemical change because it decomposes the wax into new substances such as carbon dioxide and water vapor, which cannot return to form the original wax.</p> Signup and view all the answers

    How does evaporation differ from boiling?

    <p>Evaporation is a slow process that occurs at all temperatures below a liquid's boiling point, while boiling is a rapid process that happens at a fixed temperature, the boiling point.</p> Signup and view all the answers

    What characterizes a periodic change, and can you give an example?

    <p>A periodic change occurs at regular intervals, such as the change of seasons, which happens consistently each year.</p> Signup and view all the answers

    Describe what is meant by non-periodic change and give an example.

    <p>Non-periodic change refers to alterations that do not occur at regular intervals, such as changes in weather conditions, which can be unpredictable.</p> Signup and view all the answers

    Why is the melting of wax considered a physical change?

    <p>Melting of wax is a physical change because it is temporary, reversible, and does not produce any new substances.</p> Signup and view all the answers

    Differentiate between natural changes and man-made changes, providing an example of each.

    <p>Natural changes are alterations caused by nature, like the growth of plants, while man-made changes are initiated by humans, such as the conversion of iron to steel.</p> Signup and view all the answers

    What occurs during the slow change of a tree growing from a seed?

    <p>The growth of a tree from a seed is a slow change that occurs gradually over time as the seed germinates and develops into a mature plant.</p> Signup and view all the answers

    Identify and explain an example of an undesirable change.

    <p>An example of an undesirable change is flooding caused by rain, which can lead to destruction and loss of property.</p> Signup and view all the answers

    What indicates that the transformation of milk into curd is irreversible?

    <p>The original substance, milk, cannot be changed back from curd, indicating it's an irreversible chemical change.</p> Signup and view all the answers

    How does the process of sublimation apply to ammonium chloride?

    <p>Ammonium chloride sublimates upon heating, dissociating into ammonia and hydrogen chloride gas, showcasing both physical and chemical change.</p> Signup and view all the answers

    What is the significance of the pop sound when hydrogen gas is ignited?

    <p>The pop sound indicates that hydrogen gas is combustible and produces water upon combustion, demonstrating a chemical change.</p> Signup and view all the answers

    In the heating of sugar, what happens after it changes color to reddish-brown?

    <p>After turning reddish-brown, the sugar continues to darken and eventually turns black, indicating charring, which is a chemical change.</p> Signup and view all the answers

    What can be concluded when iron and sulfur are heated together?

    <p>Heating iron and sulfur results in the formation of iron sulfide, which is a new substance, indicating a chemical change.</p> Signup and view all the answers

    Why is the dissolution of salt in water classified as a physical change?

    <p>The change is reversible, as the salt can be recovered by evaporating the water, and no new substances are formed.</p> Signup and view all the answers

    What happens when quick lime is mixed with water?

    <p>Mixing quick lime with water produces heat and a hissing sound, indicating a chemical change as new substances are formed.</p> Signup and view all the answers

    How does the melting of ice illustrate a physical change?

    <p>Melting ice to water is reversible, and both states are chemically the same substance, H2O.</p> Signup and view all the answers

    What characterizes the change from naphthalene solid to gas?

    <p>The sublimation of naphthalene is a physical change because it transforms directly from solid to gas without forming liquid.</p> Signup and view all the answers

    What does the browning of sugar during heating signify?

    <p>The browning signifies a chemical transformation where the sugar decomposes, leading to new colored compounds.</p> Signup and view all the answers

    Study Notes

    Desirable and Undesirable Changes

    • A desirable change produces a positive outcome, like rain nourishing crops.
    • An undesirable change is unfavorable, like rain causing destructive floods.

    Evaporation and Boiling

    • Evaporation is a slow process occurring at the liquid's surface, at temperatures below its boiling point.
    • Boiling is a fast process happening throughout the liquid, at its fixed boiling point.

    Periodic and Non-Periodic Changes

    • Periodic changes happen at regular intervals, for example, the change of seasons.
    • Non-periodic changes do not occur at regular intervals, like changes in weather.

    Slow and Fast Changes

    • Slow changes occur gradually over extended periods, like tree growth from a seed.
    • Fast changes happen rapidly, within seconds or minutes, like lightning.

    Natural and Man-made Changes

    • Natural changes are caused by nature, like growth in humans and plants.
    • Man-made changes are caused by humans, like converting iron into steel.

    Melting Wax vs. Burning a Candle

    • Melting wax is a physical change because it's temporary, reversible, and doesn't produce new substances.
    • Burning a candle is a chemical change because it's permanent, irreversible, and creates new substances (carbon dioxide and water vapor).

    Examples of Physical and Chemical Changes

    • Physical Changes:
      • Boiling water into vapor
      • Ice melting into water
      • Sublimation of naphthalene
      • Dissolving salt in water
    • Chemical Changes:
      • Burning paper into ash
      • Burning a candle
      • Souring milk into curd
      • Heating iron with sulfur to form iron sulfide
      • Dissolving zinc in dilute sulfuric acid

    Interconversion of Matter

    • Interconversion of matter involves changes in state, like ice to water and back to ice.
    • It's a physical change as it's reversible, no new products form, and the original substance's properties remain unchanged.

    Sublimation

    • Sublimation is the direct conversion of a solid to a gas, followed by the reverse process on cooling.
    • It's a physical change because it's reversible and doesn't produce new substances.

    Sublimation of Ammonium Chloride

    • Ammonium chloride sublimation involves a physical change (reversible change of state) and a chemical change (dissociation and recombination of molecules).

    Mixing Iron and Sulfur

    • Separating iron and sulfur from a mixture is a physical change, as it's reversible, doesn't form new products, and the mixture retains the properties of its components.
    • Heating iron and sulfur together is a chemical change, resulting in a new product (iron sulfide) with distinct properties, and it's irreversible.

    Desirable and Undesirable Changes

    • Desirable changes benefit people, like rain watering crops.
    • Undesirable changes have negative effects, like floods caused by heavy rain.

    Types of Changes

    • Evaporation is a slow process occurring at the liquid's surface, happening below the boiling point.
    • Boiling is a fast process happening throughout the liquid, occurring at a fixed temperature called the boiling point.
    • Periodic changes occur at regular intervals, for example, the change of seasons.
    • Non-Periodic changes do not occur at regular intervals, like weather changes.
    • Slow changes occur over long periods, such as a tree's growth from a seed.
    • Fast changes take place quickly, like lightning.
    • Natural changes are caused by nature, for example, the growth of humans and plants.
    • Man-made changes are caused by humans, like converting iron into steel.

    Physical and Chemical Changes

    • Melting of wax is a physical change because it is temporary, reversible, and doesn't involve the formation of new substances.
    • Burning of a candle is a chemical change because it is permanent, irreversible, and new substances (carbon dioxide & water vapour) are formed.

    Examples of Physical and Chemical Changes

    • Boiling water is a physical change.
    • Burning paper is a chemical change.
    • Ice melting is a physical change.
    • Sublimation of solid ammonium chloride is both a physical and chemical change. It involves a change of state (physical) and the formation of new products (chemical).
    • Dissolving salt in water is a physical change.
    • Reacting zinc with dilute sulfuric acid is a chemical change.
    • Separating a mixture of iron and sulphur is a physical change.
    • Heating iron and sulfur is a chemical change.

    Interconversion of Matter

    • Interconversion of matter is a physical change, involving reversible transformations between states without producing new substances and maintaining original properties.
    • Changes from ice to water and back are physical changes as they are temporary, reversible, do not result in new products, and maintain the properties of the original substance (H2O).
    • Sublimation, the direct conversion of a solid to a gas, is a physical change as it involves a reversible change of state and no new substances are formed.

    Desirable and Undesirable Changes

    • Desirable changes create positive outcomes, such as rain providing water to crops.
    • Undesirable changes are unfavorable, for example, rain causing flooding.

    Evaporation vs. Boiling

    • Evaporation is a slow process happening at the surface of a liquid, occurring at temperatures below its boiling point.
    • Boiling is a rapid process that happens throughout the liquid at its boiling point.

    Periodic and Non-Periodic Changes

    • Periodic changes occur regularly at specific intervals (e.g., changing seasons).
    • Non-periodic changes don't occur at regular intervals (e.g., weather changes).

    Slow and Fast Changes

    • Slow changes occur gradually over extended periods (e.g., tree growth).
    • Fast changes happen quickly (e.g., lightning).

    Natural and Man-Made Changes

    • Natural changes occur due to natural processes (e.g., human growth).
    • Man-made changes are caused by human actions (e.g., steel production).

    Physical vs. Chemical Changes: Examples

    • Melting wax: A physical change because it is reversible, no new substance is formed, and heat energy is absorbed and released.
    • Burning candle: A chemical change because it is irreversible, new substances are formed, and the process involves decomposition.
    • Boiling water: A physical change, as water converts to vapor and back to liquid, and no new substances are formed.
    • Burning paper: A chemical change as the paper decomposes into ash, which is irreversible.
    • Ice melting: A physical change as it is reversible, no new substances are formed, and the chemical composition remains H2O.
    • Sublimation of naphthalene: A physical change as it is reversible, no new substance is formed, and the change is simply a change of state.
    • Sublimation of ammonium chloride: This is a combination of both physical and chemical changes: physical due to the reversible change of state, and chemical due to the formation of new products (ammonia and hydrogen chloride).
    • Adding salt to water: A physical change because the salt dissolves and can be recovered, making it reversible and no new substances are formed.

    Interconversion of Matter

    • A physical change involving the transformation of matter from one state to another and back to its original state through changes in temperature or pressure.
    • This is a reversible process with no new products formed, and the original substance's properties remain unchanged.

    Chemical vs. Physical Changes: Further Examples

    • Adding dilute sulfuric acid to zinc: A chemical change due to the irreversible formation of new substances (zinc sulphate and hydrogen gas).
    • Separating iron and sulfur mixture: A physical change as it is reversible, no new substances are formed, and the mixture retains the individual properties of iron and sulfur.
    • Heating iron and sulfur: A chemical change due to the formation of a new substance (iron sulfide) with different properties, and the process is irreversible.

    Desirable and Undesirable Changes

    • Desirable changes lead to positive outcomes, for example, rain nourishing crops.
    • Undesirable changes lead to unfavorable outcomes, for example, floods caused by rain.

    Evaporation and Boiling

    • Evaporation is a slow process occurring at the liquid's surface, happening below the boiling point.
    • Boiling is a rapid process occurring throughout the liquid, happening at a fixed temperature (its boiling point).

    Periodic and Non-Periodic Changes

    • Periodic changes occur at regular intervals, like the changing seasons.
    • Non-periodic changes are not regular, like changes in weather.

    Slow and Fast Changes

    • Slow changes occur over extended periods like days, months, or years, such as tree growth.
    • Fast changes occur rapidly, within seconds or minutes, like lightning strikes.

    Natural and Man-Made Changes

    • Natural changes are caused by nature, like human and plant growth.
    • Man-made changes are initiated by humans, like converting iron into steel.

    Examples of Physical and Chemical Changes

    • Melting wax is a physical change because:
      • It is temporary and reversible.
      • No new substance is formed; it's just a change in state.
      • No significant heat absorption or release.
    • Burning a candle is a chemical change because:
      • It is permanent and irreversible.
      • New substances like carbon dioxide and water vapor are formed.
      • It involves decomposition of the wax.

    Other Examples of Physical and Chemical Changes

    • Boiling water is a physical change - reversible (condenses back to water), no new substance.
    • Burning paper is a chemical change - irreversible (ash formed), new substance (ash).
    • Ice melting is a physical change - reversible (water freezes back to ice), no new substance.
    • Ammonium chloride sublimating is both a physical and chemical change:
      • Physical: Reversible, changes state, no new substance.
      • Chemical: New substances (ammonia and hydrogen chloride) are formed, but they recombine on cooling.
    • Adding salt to water is a physical change - reversible (water evaporates leaving salt), no new substance.
    • Adding dilute sulfuric acid to zinc is a chemical change - permanent, new substances (zinc sulfate and hydrogen gas) are formed.
    • Separating iron and sulfur from a mixture is a physical change - reversible, original substances unchanged.
    • Heating iron and sulfur together is a chemical change - irreversible, new substance (iron sulfide) formed, with distinct properties.

    Interconversion of Matter

    • Interconversion is a physical change because:
      • It is reversible.
      • No new products are formed, just a change in state.
      • The original substance retains its properties.
    • Ice to water and back to ice is a physical change because:
      • It is temporary and reversible.
      • No new substances are formed (both are chemically H2O).
      • The original properties remain the same.
    • Sublimation of naphthalene is a physical change because:
      • It involves a change of state, but no new substance is formed.
      • It is reversible.

    Desirable and Undesirable Changes

    • Desirable changes are beneficial and produce positive outcomes. For example, rain providing water to crops.
    • Undesirable changes are unfavorable and have negative consequences. For example, rain causing destructive floods.

    Evaporation and Boiling

    • Evaporation is a slow process occurring at the surface of a liquid below its boiling point.
    • Boiling is a faster process occurring throughout the entire liquid at its specific boiling point.

    Periodic and Non-Periodic Changes

    • Periodic changes occur regularly at set intervals, like the change of seasons.
    • Non-periodic changes do not have a regular pattern and occur irregularly, like weather changes.

    Slow and Fast Changes

    • Slow changes take place gradually over extended periods, like the growth of a tree from a seed.
    • Fast changes happen rapidly within seconds or minutes, such as lightning.

    Natural and Man-Made Changes

    • Natural changes are events caused by nature, such as the growth of humans and plants.
    • Man-made changes are caused by human intervention, like the transformation of iron into steel.

    Melting of Wax vs. Burning of Candle

    • Melting wax is a physical change because it is temporary, reversible, and does not form new substances.
    • Burning a candle is a chemical change because it is permanent, irreversible, and produces new substances like carbon dioxide and water vapor.

    Examples of Physical and Chemical Changes

    • Physical changes involve a change in state without forming new substances, often reversible:
      • Boiling water into vapor.
      • Ice melting into water.
      • Dissolving salt in water.
      • Sublimation of naphthalene (solid to gas)
    • Chemical changes involve the formation of new substances and are usually irreversible:
      • Burning a piece of paper.
      • Burning a candle.
      • Formation of curd from milk.
      • Dissolving quick lime in water.

    Interconversion of Matter

    • Matter changing from one state to another and back (like ice to water and back) is a physical change because it's reversible, doesn't create new products, and doesn't alter the original substance's properties.

    Sublimation

    • Sublimation involves a solid directly turning into a gas without going through a liquid state (like naphthalene). This is a physical change as it's reversible and doesn't produce new substances.

    Sublimation of Ammonium Chloride

    • Ammonium chloride (NH4Cl) sublimes, releasing ammonia (NH3) and hydrogen chloride (HCl) gases.
    • This process involves both a physical change (reversible sublimation) and a chemical change (formation of new gas products).

    Sodium Chloride in Water

    • Dissolving salt in water is a physical change because it's:
      • Temporary and reversible (salt can be recovered by evaporation).
      • Doesn't form new substances.

    Dilute Sulphuric Acid and Zinc

    • This reaction is a chemical change because:
      • It's permanent and irreversible.
      • New substances are formed: zinc sulphate and hydrogen gas.

    Iron and Sulphur mixture vs. Iron Sulphide

    • Mixing iron and sulphur is a physical change because:
      • The process is reversible.
      • No new substances are formed.
    • Heating iron and sulfur together to form iron sulphide is a chemical change because:
      • It creates a new substance with different properties.
      • The process is irreversible.

    Desirable and Undesirable Changes

    • Desirable changes result in positive outcomes, like rain nourishing crops.
    • Undesirable changes have negative consequences, such as floods caused by excessive rain.

    Evaporation and Boiling

    • Evaporation is a gradual process occurring on a liquid's surface at temperatures below its boiling point.
    • Boiling is a rapid process happening throughout the liquid at its fixed boiling point.

    Periodic and Non-Periodic Changes

    • Periodic changes occur at regular intervals, like the change of seasons.
    • Non-periodic changes are irregular and do not repeat at set intervals, exemplified by weather changes.

    Slow and Fast Changes

    • Slow changes occur gradually over extended periods, such as tree growth from a seed.
    • Fast changes happen quickly, measured in seconds or minutes, like a lightning strike.

    Natural and Man-Made Changes

    • Natural changes are driven by forces of nature, such as the growth of humans and plants.
    • Man-made changes are brought about by human intervention, like turning iron into steel.

    Physical and Chemical Changes

    • Melting wax is a temporary, reversible physical change.
    • Burning a candle is a permanent, irreversible chemical change, producing carbon dioxide and water vapor.
    • Examples of physical changes:
      • Boiling water into vapor
      • Ice cubes melting into water
      • Sublimation of naphthalene
      • Adding salt to water
    • Examples of chemical changes:
      • Burning paper into ash
      • Milk turning into curd
      • Heating iron and sulfur to create iron sulfide
      • Reacting zinc with dilute sulfuric acid

    Important Notes

    • Interconversion of matter involves changes in state, like ice to water and vice versa, which are physical changes.
    • Sublimation, the direct conversion of a solid to a gas, can involve both physical and chemical aspects.
    • The formation of a new substance with distinct properties often indicates a chemical change.

    Desirable and Undesirable changes

    • Desirable changes produce positive results.
    • Undesirable changes are unfavorable.

    Evaporation and Boiling

    • Evaporation is a gradual process occurring at the surface of a liquid, below the boiling point.
    • Boiling is a rapid process occurring throughout the liquid, at a fixed temperature, the boiling point.

    Periodic and Non-Periodic Changes

    • Periodic changes occur regularly at specific intervals, like the change of seasons.
    • Non-periodic changes are irregular and do not repeat at set intervals, like changes in weather.

    Slow and Fast Changes

    • Slow changes take place over extended periods, like tree growth from a seed.
    • Fast changes happen quickly, within seconds or minutes, like lightning.

    Natural and Man-Made Changes

    • Natural changes are caused by nature, like human and plant growth.
    • Man-made changes are caused by human actions, like converting iron into steel.

    Melting vs. Burning of Wax

    • Melting is a temporary and reversible process.
    • Burning is a permanent and irreversible process.
    • Melting involves heat absorption and release, maintaining the original substance.
    • Burning involves decomposition of wax, forming new substances that cannot be recombined.
    • No new substance forms during melting; the original and final product is wax.
    • Burning produces new substances like carbon dioxide and water vapor.

    Examples of Physical and Chemical Changes

    • Boiling water: Physical change, as it's reversible and forms the same substance, water.
    • Burning paper: Chemical change, as it's irreversible with the formation of ash, a new substance.
    • Ice melting: Physical change, due to its temporary nature and no new substance formation.
    • Ammonium chloride sublimation: A combination of both physical and chemical changes. It's reversible and the original substance is regained, but during the process, new products are formed, ammonia, and hydrogen chloride.
    • Salt dissolving in water: Physical change, as dissolving is reversible and no new substance forms.
    • Zinc reacting with dilute sulfuric acid: Chemical change, as it's irreversible and produces zinc sulfate and hydrogen gas.
    • Iron and sulfur mixture: Physical change, as it's reversible and no new substance forms.
    • Heating a mixture of iron and sulfur: Chemical change, as it's irreversible and forms a new substance, iron sulfide, with properties different from iron and sulfur.

    Interconversion of Matter

    • It involves changes in the state of matter but no new substance is created. It's reversible, altering temperature or pressure.
    • This is considered a physical change because it's reversible, does not form new products, and does not change the original substance's properties.

    Sublimation of Naphthalene

    • It's a physical change involving a state change (solid to gas) and back, without a liquid phase.
    • This is reversible and no new substance is formed.

    Chemical Changes in Milk

    • Milk turning into curd is a chemical change.
    • It's irreversible and forms a new substance, curd.

    Desirable and Undesirable Change

    • Desirable changes produce favorable outcomes, while undesirable changes have unfavorable outcomes.
    • Example of desirable change: Rain bringing water to crops.
    • Example of undesirable change: Rain causing destruction by floods.

    Evaporation and Boiling

    • Evaporation is a slow process that occurs at the surface of a liquid below its boiling point.
    • Boiling is a fast process that occurs throughout the liquid at a fixed temperature, the boiling point.

    Periodic and Non-Periodic Change

    • Periodic changes occur at regular intervals, such as the change of seasons.
    • Non-periodic changes do not occur at regular intervals, such as changes in weather.

    Slow and Fast Change

    • Slow changes occur over extended periods, such as the growth of a tree.
    • Fast changes occur rapidly, like the occurrence of lightning.

    Natural and Man-Made Change

    • Natural changes are brought about by nature, such as the growth of humans and plants.
    • Man-made changes are caused by human actions, such as converting iron to steel.

    Physical and Chemical Changes

    • Melting of wax is a physical change, while burning a candle is a chemical change.
    • Melting of wax is temporary and reversible, while burning a candle is permanent and irreversible.
    • During melting, heat is absorbed and released resulting in the original substance.
    • During burning, the wax decomposes into new substances that cannot be recombined.
    • No new substances are formed during melting, while burning produces new substances (CO2 and water vapor).

    Examples of Physical and Chemical Changes

    • Physical Changes:
      • Boiling water, which turns into vapor.
      • Sublimation of naphthalene, which directly transitions from solid to gas.
      • Dissolving sodium chloride (salt) in water, which can be reversed by evaporation.
      • Adding salt to water, which forms a solution and can be reversed.
      • The interconversion of matter, where a substance changes state (e.g., ice to water) and back to its original state, a reversible process with no new products formed.
    • Chemical Changes:
      • Burning paper, which turns into ash.
      • Heating a piece of iron with sulfur, which forms iron sulfide, a new substance with different properties.
      • Adding dilute sulfuric acid to zinc, which results in the formation of zinc sulfate and hydrogen gas.
      • Dissociation of ammonium chloride (NH4Cl) upon heating, which produces ammonia (NH3) and hydrogen chloride (HCl), which recombine upon cooling.
      • Milk turning into curd.

    Sublimation

    • Sublimation is the direct conversion of a solid into a gaseous state without passing through the liquid state.
    • It is a reversible process, as the gas can condense back into the solid state.

    Dissociation

    • Dissociation involves the formation of new products from a single substance.
    • It is a chemical change due to the creation of new substances.

    Mixtures vs. Compounds

    • A mixture is a physical combination of substances with no new substance formed.
    • It can be separated by physical means, and its properties are similar to the individual substances.
    • A compound is a chemical combination of substances forming a new substance with different properties.
    • It cannot be separated by physical means, and its properties differ from the individual substances.

    Summary of Physical and Chemical Changes

    • Physical Change:
      • Reversible, temporary change
      • No new substances are formed
      • Original substance's properties remain unchanged
    • Chemical Change:
      • Irreversible, permanent change
      • New substances are formed with different properties
      • Original substances' properties are altered.

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    Description

    Test your knowledge on various types of changes in nature and human impacts. This quiz covers desirable versus undesirable changes, evaporation and boiling, and the distinctions between periodic and non-periodic changes. Understand how these concepts apply in everyday life and the environment.

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