Chemical Reactions and Equations Chapter 1
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Questions and Answers

What is the product formed when magnesium ribbon burns in air?

magnesium oxide

Which of the following observations help determine whether a chemical reaction has taken place?

  • evolution of a gas (correct)
  • change in colour (correct)
  • change in temperature (correct)
  • change in state (correct)

    • A chemical equation represents a ____________.

    chemical reaction

    The law of conservation of mass states that mass can be created in a chemical reaction.

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

    What is the process called when the number of atoms of each element is equal on both sides of a chemical equation?

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

    Why should a magnesium ribbon be cleaned before burning in air?

    <p>To remove the oxide layer and ensure a cleaner reaction</p> Signup and view all the answers

    Write the balanced equation for the chemical reaction: Hydrogen + Chlorine → Hydrogen chloride

    <p>H2 + Cl2 → 2HCl</p> Signup and view all the answers

    Write the balanced equation for the chemical reaction: Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride

    <p>3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3</p> Signup and view all the answers

    Write the balanced equation for the chemical reaction: Sodium + Water → Sodium hydroxide + Hydrogen

    <p>2Na + 2H2O → 2NaOH + H2</p> Signup and view all the answers

    Write a balanced chemical equation with state symbols for the reaction where solutions of barium chloride and sodium sulphate in water react.

    <p>BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)</p> Signup and view all the answers

    Write a balanced chemical equation with state symbols for the reaction where sodium hydroxide solution reacts with hydrochloric acid solution.

    <p>NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)</p> Signup and view all the answers

    What form of energy is causing the decomposition reactions in silver chloride and silver bromide when exposed to sunlight?

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

    What do you feel when you touch the bottom of the test tube after mixing barium hydroxide and ammonium chloride?

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

    Why does the iron nail become brownish in color and the blue color of copper sulfate solution fade?

    <p>displacement reaction</p> Signup and view all the answers

    What type of reaction is represented by the formation of BaSO4 in Activity 1.10?

    <p>precipitation reaction</p> Signup and view all the answers

    What is the term for reactions where there is an exchange of ions between reactants?

    <p>double displacement reactions</p> Signup and view all the answers

    If a substance gains oxygen during a reaction, what term is used to describe this process?

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

    If a substance loses oxygen during a reaction, what term is used to describe this process?

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

    What is the common term for the process where metals get coated with a reddish-brown powder when left exposed?

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

    Which of the statements about the reaction 2PbO(s) + C(s) → 2Pb(s) + CO2(g) are incorrect?

    <p>Carbon is getting oxidised.</p> Signup and view all the answers

    The reaction Fe2O3 + 2Al → Al2O3 + 2Fe is an example of a

    <p>combination reaction.</p> Signup and view all the answers

    What happens when dilute hydrochloric acid is added to iron fillings?

    <p>Hydrogen gas and iron chloride are produced.</p> Signup and view all the answers

    What is a balanced chemical equation? Why should chemical equations be balanced?

    <p>A balanced chemical equation has an equal number of atoms of each element on both sides of the equation. Chemical equations should be balanced to satisfy the law of conservation of mass.</p> Signup and view all the answers

    Translate the following statements into chemical equations and then balance them: (a) Hydrogen gas combines with nitrogen to form ammonia. (b) Hydrogen sulphide gas burns in air to give water and sulfur dioxide. (c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate. (d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

    <p>Provide balanced chemical equations for each of these statements.</p> Signup and view all the answers

    What does one mean by exothermic and endothermic reactions? Give examples.

    <p>Exothermic reactions release heat or energy to the surroundings, while endothermic reactions absorb heat or energy from the surroundings. An example of an exothermic reaction is combustion, while an example of an endothermic reaction is photosynthesis.</p> Signup and view all the answers

    A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

    <p>element: Copper, compound formed: Copper oxide</p> Signup and view all the answers

    Why do we apply paint on iron articles?

    <p>Paint is applied on iron articles to prevent them from rusting by forming a protective barrier between the iron and atmospheric oxygen and moisture.</p> Signup and view all the answers

    Oil and fat containing food items are flushed with nitrogen. Why?

    <p>Flushing oil and fat containing food items with nitrogen helps prevent oxidation and rancidity by removing oxygen from the packaging environment.</p> Signup and view all the answers

    Explain the following terms with one example each: (a) Corrosion (b) Rancidity

    <p>(a) Corrosion is the gradual destruction of materials by chemical or electrochemical reaction with their environment. Example: Rusting of iron. (b) Rancidity is the spoilage of food products through the chemical decomposition of fats and oils. Example: Spoilage of cooking oils.</p> Signup and view all the answers

    Study Notes

    Chemical Reactions and Equations

    • Chemical reactions involve the breaking and making of bonds between atoms to produce new substances.
    • A chemical reaction is determined by observing:
      • Change in state
      • Change in color
      • Evolution of a gas
      • Change in temperature

    Chemical Equations

    • A chemical equation is a symbolic representation of a chemical reaction.
    • A word-equation is a sentence form of a chemical equation.
    • Example of a word-equation: Magnesium + Oxygen → Magnesium oxide
    • A chemical equation can be written in a shorter form using chemical formulae.
    • Example: Mg + O2 → MgO

    Balanced Chemical Equations

    • A balanced chemical equation has the same number of atoms of each element on both the reactant and product sides.
    • The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction.
    • Steps to balance a chemical equation:
      1. Draw boxes around each formula.
      2. List the number of atoms of different elements present in the unbalanced equation.
      3. Balance the atoms by adding coefficients.
      4. Check the correctness of the balanced equation.

    Writing Symbols of Physical States

    • Physical states of reactants and products can be represented by:
      • (g) for gas
      • (l) for liquid
      • (aq) for aqueous (solution in water)
      • (s) for solid
    • Example: 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

    Types of Chemical Reactions

    • Combination reactions: when two or more substances combine to form a single product.
      • Example: CaO(s) + H2O(l) → Ca(OH)2(aq)
    • Decomposition reactions: when a single reactant breaks down to give simpler products.
      • Example: 2FeSO4(s) → Fe2O3(s) + SO2(g) + SO3(g)
    • Exothermic reactions: reactions that release heat along with the formation of products.
      • Examples: burning of coal, formation of water, respiration, and decomposition of vegetable matter.### Decomposition Reactions
    • Decomposition reaction is a type of reaction where a single substance breaks down into two or more substances.
    • Example: Calcium carbonate (CaCO3) decomposes into calcium oxide (CaO) and carbon dioxide (CO2) when heated.
    • This reaction is an example of thermal decomposition, which is a type of decomposition reaction that occurs when a substance is heated.

    Thermal Decomposition

    • Thermal decomposition is a type of decomposition reaction that occurs when a substance is heated.
    • Example: Lead nitrate (Pb(NO3)2) decomposes into lead oxide (PbO), nitrogen dioxide (NO2), and oxygen (O2) when heated.
    • Another example: Silver chloride (AgCl) decomposes into silver (Ag) and chlorine (Cl2) when exposed to sunlight.

    Displacement Reactions

    • Displacement reaction is a type of reaction where an element displaces another element from its compound.
    • Example: Iron (Fe) displaces copper (Cu) from copper sulphate (CuSO4) solution, resulting in iron sulphate (FeSO4) and copper (Cu).
    • Other examples: Zinc (Zn) displaces copper (Cu) from copper sulphate (CuSO4) solution, and lead (Pb) displaces copper (Cu) from copper chloride (CuCl2) solution.

    Double Displacement Reactions

    • Double displacement reaction is a type of reaction where two different atoms or groups of atoms (ions) are exchanged.
    • Example: Sodium sulphate (Na2SO4) and barium chloride (BaCl2) react to form barium sulphate (BaSO4) and sodium chloride (NaCl).
    • This reaction is an example of a precipitation reaction, where a white precipitate of barium sulphate is formed.

    Oxidation and Reduction

    • Oxidation is the gain of oxygen or loss of hydrogen.
    • Reduction is the loss of oxygen or gain of hydrogen.
    • Example: Copper (Cu) oxidizes to form copper oxide (CuO) when heated in air, and reduces back to copper (Cu) when hydrogen gas (H2) is passed over it.

    Corrosion

    • Corrosion is the process of a metal being attacked by substances around it, such as moisture and acids.
    • Example: Iron rusts when exposed to air and moisture, forming a reddish-brown coating of iron oxide.

    Rancidity

    • Rancidity is the process of oxidation of fats and oils, resulting in a change in their smell and taste.
    • Example: Fats and oils in food can become rancid when exposed to air, resulting in an unpleasant smell and taste.

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