Physical and Chemical Changes
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Questions and Answers

Which of the following is an example of a physical change?

  • Burning wood
  • Cooking an egg
  • Melting ice (correct)
  • Rusting of iron

What type of change alters the form or appearance of a substance but does not change its chemical composition?

  • Physical change (correct)
  • Chemical change
  • Ionic change
  • Nuclear change

What is the process of a solid changing directly into a gas called?

  • Freezing
  • Melting
  • Sublimation (correct)
  • Condensation

Which of the following is a sign of a chemical change?

<p>Gas formation (B)</p> Signup and view all the answers

In a chemical equation, what are the substances on the left side of the arrow called?

<p>Reactants (C)</p> Signup and view all the answers

What type of reaction involves a substance reacting rapidly with oxygen to produce heat and light?

<p>Combustion reaction (D)</p> Signup and view all the answers

Which of the following factors usually increases the rate of a chemical reaction?

<p>Increasing temperature (D)</p> Signup and view all the answers

What principle states that mass is neither created nor destroyed in a chemical reaction?

<p>Law of conservation of mass (C)</p> Signup and view all the answers

Which of the following is a physical property of a substance?

<p>Color (B)</p> Signup and view all the answers

Flashcards

Physical Change

Alterations that do not change the chemical identity of a substance, often involving changes in size, shape, or state. The chemical formula remains the same and are often reversible.

Melting

The change from a solid to a liquid state.

Freezing

The change from a liquid to a solid state.

Boiling

The change from a liquid to a gas state.

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Condensation

The change from a gas to a liquid state.

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Sublimation

The change from a solid directly to a gas state.

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Chemical Change

Involves the rearrangement of atoms and molecules to form new substances with different properties. They are typically irreversible without further reactions.

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Combination (Synthesis) Reactions

Two or more reactants combine to form a single product (A + B → AB).

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Decomposition Reactions

A single reactant breaks down into two or more products (AB → A + B).

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Exothermic Reactions

Reactions that release energy, usually in the form of heat or light, resulting in a decrease in the system's energy.

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Study Notes

  • Physical and chemical changes are fundamental concepts describing matter alteration.
  • Physical changes affect a substance's form without changing its chemical composition.
  • Chemical changes rearrange atoms and molecules, forming new substances.

Physical Changes

  • These do not alter the chemical identity of a substance.
  • They often involve changes in size, shape, or state.
  • Examples: changes of state (melting, freezing, boiling, condensation, sublimation), tearing, crushing, dissolving.
  • The chemical formula remains constant during a physical change.
  • Physical changes are often reversible.

States of Matter

  • Matter exists as solid, liquid, gas, and plasma.
  • Transitions between these states are physical changes.
  • Melting: solid to liquid at the melting point.
  • Freezing: liquid to solid at the freezing point.
  • Boiling: liquid to gas at the boiling point.
  • Condensation: gas to liquid.
  • Sublimation: solid directly to gas.
  • Deposition: gas directly to solid.

Dissolving

  • This is a physical change where a solute disperses in a solvent.
  • The solute's chemical identity remains unchanged.
  • Example: Sugar (C12H22O11) dissolving in water remains sugar molecules surrounded by water.
  • The process is reversible through evaporation.

Chemical Changes

  • Also known as chemical reactions, they rearrange atoms and molecules to form new substances.
  • These are typically irreversible without further reactions.
  • Indicators: color change, gas formation, precipitate formation, heat absorption (endothermic) or release (exothermic), and light emission.
  • Examples include burning, rusting, cooking, and neutralization reactions.
  • Reactants convert into products during these.

Chemical Equations

  • These represent chemical reactions.
  • Reactants are on the left, products on the right, separated by an arrow.
  • Example: 2H2 + O2 → 2H2O (hydrogen gas + oxygen gas forms water).
  • Balancing ensures the number of atoms of each element is the same on both sides.

Types of Chemical Reactions

  • Combination (Synthesis): A + B → AB
  • Decomposition: AB → A + B
  • Single Displacement: A + BC → AC + B
  • Double Displacement: AB + CD → AD + CB
  • Combustion: a substance reacts rapidly with oxygen, producing heat and light.
  • Acid-Base Neutralization: an acid reacts with a base to form a salt and water.

Evidence of Chemical Changes

  • Color Change: indicates a new substance.
  • Gas Formation: bubbles indicate gas release (not boiling).
  • Precipitate Formation: a solid forming when two solutions are mixed.
  • Heat Absorption or Release: endothermic cools, exothermic heats.
  • Light Emission: strong indicator of a chemical reaction.

Examples of Physical Changes

  • Melting ice: solid to liquid water (H2O).
  • Boiling water: liquid to steam (H2O).
  • Chopping wood: changes size and shape, remains wood.
  • Dissolving salt in water: salt disperses, retains original properties.
  • Bending a metal rod: changes shape, same composition.

Examples of Chemical Changes

  • Burning wood: forms ash, carbon dioxide, and water.
  • Rusting of iron: forms iron oxide.
  • Cooking an egg: proteins denature and solidify.
  • Baking a cake: reactions produce new compounds.
  • Neutralizing acid with a base: HCl + NaOH → NaCl + H2O.

Factors Affecting the Rate of Chemical Reactions

  • Temperature: Higher temperature increases reaction rate.
  • Concentration: Higher concentration generally increases reaction rate.
  • Surface Area: Increased surface area increases reaction rate.
  • Catalysts: speed up reactions without being consumed.
  • Pressure: Increasing pressure can increase reaction rate for gases.

Conservation of Mass

  • Mass is neither created nor destroyed in a chemical reaction.
  • Total reactant mass equals total product mass.
  • Essential for balancing equations.
  • During physical changes, mass remains constant.

Energy Changes

  • Chemical reactions involve energy changes.
  • Exothermic reactions release energy, decreasing the system's energy.
  • Endothermic reactions absorb energy, increasing the system's energy.
  • Enthalpy change (ΔH) quantifies energy change: negative for exothermic, positive for endothermic.

Physical vs. Chemical Properties

  • Physical properties: observed without changing chemical identity (color, density, melting point, boiling point).
  • Chemical properties: describe reactions with other substances (flammability, reactivity with acids, oxidizing ability).
  • Physical changes alter physical properties, and chemical changes alter chemical properties.

Applications in Daily Life

  • Crucial in cooking, cleaning, industrial processes, and environmental science.
  • Cooking: melting butter (physical), and baking a cake (chemical).
  • Cleaning products: uses chemical reactions to remove stains.
  • Industrial processes: manufacturing plastics and pharmaceuticals depend on reactions.
  • Environmental science: used to understand pollution and climate change.

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Description

Explore physical and chemical changes, focusing on alterations to matter. Physical changes affect form without altering chemical composition, while chemical changes create new substances by rearranging atoms and molecules. Learn about states of matter and their transitions.

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