Chapter 1
Chemical Reactions and Equations
Class X
EXERCISE SOLUTION
Question 1:
Which of the 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.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Answer 1:
(i)(a) and (b)
Question 2:
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
Answer 2:
(d) The given reaction is an example of a displacement reaction.
Question 3:
What happens when dilute hydrochloric acid is added to iron filings? 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.
Answer 3:
(a) Hydrogen gas and iron chloride are produced. The reaction is as follows:
Question 4:
What is a balanced chemical equation? Why should chemical equations be balanced?
Answer 4:
A reaction which has an equal number of atoms of all the elements on both sides of the chemical equation is called a balanced chemical equation. The law of conservation of mass states that mass can neither be created nor destroyed. Hence, in a chemical reaction, the total mass of reactants should be equal to the total mass of the products. It means that the total number of atoms of each element should be equal on both sides of a chemical equation. Hence, it is for this reason that chemical equations should be balanced.
Question 5:
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 sulphur 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.
Answer 5:
(a) 3H2(g) + N2(g) → 2NH3(g)
(b) 2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
(c) 3BaCl2(aq) + Al2(SO4)3(aq) → 2AlCl3(aq) + 3BaSO4(s)
(d) 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
Question 6:
Balance the following chemical equations.
(a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Answer 6:
(a) 2HNO3 + Ca(OH)2 → NaSO4 + 2H2O
(b) 2HaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
Question 7:
Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Answer 7:
(a) Ca(OH)2 + CO2 → CaCO3 + H2O
(b) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
(c) 2Al + 3CuCl2 → 2AlCl3 + 3Cu
(d) BaCl2 + K2SO4 → BaSO4 + 2KCl
Question 8:
Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a)Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide(s)
(b) Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g)
(c) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)
Question 9:
What does one mean by exothermic and endothermic reactions? Give examples.
Answer 9:
Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions.
Example: Mixture of sodium and chlorine to yield table salt
Na(s) + 1/2Cl2(s) → NaCl(s) + 411 kJ of energy
In other words, combination reactions are exothermic. Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
For example: In the process of photosynthesis, plants use the energy from the sun to convert carbon dioxide and water to glucose and oxygen.
6CO2(g) + 6H2O(l) (sunlight)→ C6H12O6(aq) (Glucose) + 6O2(g)
Question 10:
Why is respiration considered an exothermic reaction? Explain.
Answer 10:
Energy is required to support life. Energy in our body is obtained from the food we eat. During digestion, large molecules of food are broken down into simpler substances such as glucose. Glucose combines with oxygen in the cells and provides energy. The special name of this combustion reaction is respiration. Since energy is released in the whole process, it is an exothermic process.
C6H12O6(aq) (Glucose) + 6O2(g) (Oxygen) → 6CO2(g) (Carbon dioxide) + 6H2O(l) (Water) + Energy
Question 11:
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer 11:
Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.
Decomposition reaction: AB + Energy → A + B
2H2O(l) (Electrolysis) → 2H2(g) + O2(g)
Combination reaction: A+B → AB + Energy
2H2(g) + O2(g) → 2H2O(l) + Energy
Question 12:
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Answer 12:
(a) Thermal decomposition: 2FeSO4(s) (Ferrous sulphate) \(\overset{\Delta}{\longrightarrow}\) Fe2O3(s) (Ferric oxide) + SO2(g) (Sulphur dioxide) + SO3(g) (Sulphur trioxide)
(b) Decomposition by light: 2AgCl(s) (Silver chloride) \(\overset{light}{\longrightarrow}\) 2Ag(s) (Silver) + Cl2(s) (Chlorine)
(c) Decomposition by electricity: 2Al2O3(aq) (Aluminium oxide) \(\overset{electricity}{\longrightarrow}\) 4Al(s) (Aluminium) + 3O2(g) (Oxygen)
Question 13:
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer 13:
In a displacement reaction, a more reactive element replaces a less reactive element from a compound.
A + BX → AX + B; where A is more reactive than B
In a double displacement reaction, two atoms or a group of atoms switch places to form new compounds.
AB + CD → AD + CB
For example:
Displacement reaction: CuSO4(aq) + Zn(s) → ZnSO4(aq) + Cu(s)
Double displacement reaction: NaSO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
Question 14:
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Answer 14:
2AgNO3(aq) (Silver nitrate) + Cu(s) (Copper) → Cu(NO3)2(aq) (Copper nitrate) + 2Ag(s) (Silver)