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WORKSHEET 1- Chemical Reactions and Equations

1.  Which of the given statements about the reaction below are incorrect?

a. Lead is getting reduced
b. Carbon dioxide is getting oxidised
c. Carbon is getting oxidised
d. Lead oxide is getting reduced

  • Solution:i) (a) and (b)
 2.  Fe2O3 + 2Al  Al2O3 + 2Fe

The above reaction is an example of a 
(i). Combination reaction
(ii). Double displacement reaction
(iii). Decomposition reaction
(iv). Displacement reaction
  • Solution:(iv) Displacement reaction
 3.  What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
a. Hydrogen gas and iron chloride are produced
b. Chlorine gas and iron hydroxide are produced
c. No reaction takes place
d Iron salt and water are produced
  • Solution:Hydrogen gas and iron chloride are produced
 4.  What is a balanced chemical equation? Why should chemical equations be balanced?
  • Solution:An equation for a chemical reaction is an equation in which the number of atoms for each element in the reaction and the total charge are the same for both the reactants and the products. In other words, the mass and the charge are balanced on both sides of the reaction.
 5.  Translate the following statements into chemical equations and then balance them.

  • Solution:a. 3H2 + N2 ® 2NH3
    b. 2H2S + 3O2 ® 2H2O + 2SO2
    c. 3BaCl2 + Al2(SO4)3 ® 2AlCl3 + 3BaSO4
    d. 2K + 2H2O ® 2KOH + H2
 6.  Balance the following chemical equations.
b. 
c. 

  • Solution:a. 
    b. 
    c. 
    d. 
 7.  Write the balanced chemical equations for the following reactions:
a. Calcium hydroxide + Carbon dioxideCalcium carbonate + Water
b. Zinc + Silver nitrate  Zinc nitrate + Silver
c. Aluminium + Copper chlorideAluminium chloride + Copper

  • Solution:a. 
    b. 
    c. 
    d. 
 8.  Write the balanced chemical equation for the following and identify the type of reaction of each case.a. 
b. 
c. 

  • Solution:
    a. 2KBr + BaI2 ® 2KI + BaBr2 -- Double Displacement reaction
    b. ZnCO3 ® ZnO + CO2 -- Decomposition reaction
    c. H2 + Cl2 ® 2HCl -- Combination reaction
    d. Mg + 2HCl ® MgCl2 + H2  -- Displacement reaction
 9.  What is meant by exothermic and endothermic reactions? Give examples.
  • Solution:An exothermic reaction is one that releases heat.
    Reactants Product + Energy
    A simple example of this can be seen in the combustion of hydrogen and oxygen, which is a commonly used reaction in rocket engines:
    2H2 + O2  2H2O + heat
    The result is simply water vapour.
    An endothermic process describes a reaction that absorbs energy in the form of heat.
    Example:
    N2 + O2 + Heat  2NO
    If 1 mole of N2 molecule reacts with 1 mole of O2 molecule, the heat of 184 KJ has to be supplied to initiate the reaction to give 1 mole of NO molecule. This means that the bonds between N – N and O – O are so strong that they do not break easily. N2 has triple covalent bond between the two N atoms. O2 has a double covalent bond. Thus energy has to be put into the reaction to break the strong bonds. Thus the above reaction is a good example of an endothermic reaction.
 10.  Why is respiration considered an exothermic reaction?
  • Solution:During respiration, glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy.
    Glucose + oxygen  carbon dioxide + water + energy
    It is an exothermic reaction, because energy is produced during this process.

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