Class 10 Chemical Reactions and Equations - Notes
1. Which of the statements about the reaction below are incorrect?
Answer: (i) (a) and (b) are incorrect.
2. Fe2O3 + 2Al → Al2O3 + 2Fe
Answer: (d) displacement reaction.
3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
Answer: (a) Hydrogen gas and iron chloride are produced.
4. What is a balanced chemical equation? Why should chemical equations be balanced?
Answer: A balanced chemical equation has the same number of atoms of each element on both sides. Equations should be balanced to follow the law of conservation of mass.
5. Translate the following statements into chemical equations and then balance them.
(a) N2 + 3H2 → 2NH3
(b) 2H2S + 3O2 → 2H2O + 2SO2
(c) 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
(d) 2K + 2H2O → 2KOH + H2
6. Balance the following chemical equations.
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) Already balanced.
(d) Already balanced.
7. Write the balanced chemical equations for the following reactions.
(a) Ca(OH)2 + CO2 → CaCO3 + H2O
(b) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
(c) 2Al + 3CuCl2 → 2AlCl3 + 3Cu
(d) BaCl2 + K2SO4 → BaSO4 + 2KCl
8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) 2KBr(aq) + BaI2(aq) → 2KI(aq) + BaBr2(s) - Double displacement
(b) ZnCO3(s) → ZnO(s) + CO2(g) - Decomposition
(c) H2(g) + Cl2(g) → 2HCl(g) - Combination
(d) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) - Displacement
9. What does one mean by exothermic and endothermic reactions? Give examples.
Answer: Exothermic reactions release heat (e.g., burning coal). Endothermic reactions absorb heat (e.g., photosynthesis).
10. Why is respiration considered an exothermic reaction? Explain.
Answer: Respiration releases heat when glucose reacts with oxygen in our body, making it exothermic.
11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer: Combination reactions join substances into one, decomposition reactions break one into many.
Example: 2H2 + O2 → 2H2O (Combination)
2H2O → 2H2 + O2 (Decomposition)
12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Heat: CaCO3 → CaO + CO2
Light: 2AgCl → 2Ag + Cl2
Electricity: 2H2O → 2H2 + O2
13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer: Displacement: one element replaces another (Zn + CuSO4 → ZnSO4 + Cu). Double displacement: ions exchange (AgNO3 + NaCl → AgCl + NaNO3).
14. In the refining of silver, the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.
Answer: Cu + 2AgNO3 → Cu(NO3)2 + 2Ag
15. What do you mean by a precipitation reaction? Explain by giving examples.
Answer: A precipitation reaction forms an insoluble solid in a solution. Example: BaCl2 + H2SO4 → BaSO4 (solid) + 2HCl
16. Explain the following in terms of gain or loss of oxygen with two examples each:
(a) Oxidation: gain of oxygen (2Mg + O2 → 2MgO, C + O2 → CO2)
(b) Reduction: loss of oxygen (CuO + H2 → Cu + H2O, ZnO + C → Zn + CO)
17. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Answer: 'X' is copper (Cu), and the black compound is copper oxide (CuO).
18. Why do we apply paint on iron articles?
Answer: To prevent rusting by stopping air and moisture from reaching the iron.
19. Oil and fat containing food items are flushed with nitrogen. Why?
Answer: To prevent oxidation and rancidity, keeping food fresh.
20. Explain the following terms with one example each.
(a) Corrosion: rusting of iron.
(b) Rancidity: chips becoming smelly when exposed to air.
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