Physical and Chemical Equilibrium - UNSOLVED PRACTICE SET
Chapter: Equilibrium | Topic: Physical and Chemical Equilibrium
PHYSICAL AND CHEMICAL EQUILIBRIUM - UNSOLVED PRACTICE SET
Topic: Physical and Chemical Equilibrium
Multiple Choice Questions
Q1. Which of the following is an example of a physical equilibrium?
- Decomposition of calcium carbonate
- Dissolution of sugar in water until saturation
- Combustion of methane
- Rusting of iron
Q2. In a chemical equilibrium, the rate of the forward reaction:
- Is always greater than the rate of the backward reaction
- Is always less than the rate of the backward reaction
- Becomes equal to the rate of the backward reaction
- Becomes zero
Q3. The equilibrium between ice and water at 0°C is an example of:
- Only chemical equilibrium
- Only physical equilibrium
- Both physical and chemical equilibrium
- Neither physical nor chemical equilibrium
Q4. Which of the following represents a homogeneous equilibrium?
- CaCO₃(s) ⇌ CaO(s) + CO₂(g)
- N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
- H₂O(l) ⇌ H₂O(g)
- NaCl(s) ⇌ NaCl(aq)
Q5. At equilibrium, the concentrations of reactants and products:
- Become zero
- Become equal
- Remain constant but not necessarily equal
- Keep changing continuously
Q6. The equilibrium H₂O(l) ⇌ H₂O(g) is established in a closed container. If more water vapour is added to the container, what happens?
- Some vapour condenses to liquid until equilibrium is re-established
- All vapour condenses to liquid
- More liquid evaporates
- Nothing happens; equilibrium cannot be re-established
Short Answer Questions
Q7. Distinguish between physical equilibrium and chemical equilibrium with one example for each.
Q8. Explain why a chemical equilibrium is called a 'dynamic equilibrium.' What does the term 'dynamic' signify in this context?
Q9. A student opens a bottle of cold drink and observes bubbles forming vigorously. Explain this observation in terms of equilibrium. What type of equilibrium exists in a sealed bottle of cold drink?
Q10. Write the characteristics of a system at chemical equilibrium. Why is chemical equilibrium considered reversible in nature?
Q11. In the equilibrium N₂O₄(g) ⇌ 2NO₂(g), the colour of the mixture becomes constant after some time. Explain why the colour remains constant even though the reaction is still occurring.
Q12. Give two examples of physical equilibrium from daily life and explain how they demonstrate the concept of equilibrium.
Long Answer Questions
Q13. (a) Define physical equilibrium and chemical equilibrium with suitable examples.
(b) Explain the characteristics of chemical equilibrium with reference to the reaction: H₂(g) + I₂(g) ⇌ 2HI(g)
(c) A student argues that at equilibrium, the forward and backward reactions stop completely. Is the student correct? Explain with reasoning.
Q14. (a) Explain what is meant by 'dynamic nature of chemical equilibrium' with a suitable example.
(b) Describe an experiment to demonstrate that chemical equilibrium is dynamic and not static.
(c) For the equilibrium 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), explain what happens at the molecular level when equilibrium is established.
Q15. (a) Classify the following equilibria as homogeneous or heterogeneous. Give reasons for your classification:
(i) 2NO(g) + O₂(g) ⇌ 2NO₂(g)
(ii) CaCO₃(s) ⇌ CaO(s) + CO₂(g)
(iii) NH₃(g) + HCl(g) ⇌ NH₄Cl(s)
(iv) CH₃COOH(l) + C₂H₅OH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l)
(b) In the Indian context, give one example each of physical and chemical equilibrium from everyday life (kitchen, household, or agriculture) and explain the equilibrium involved.
Numerical / Application-Based Problems
Q16. A sealed 2.0 L container contains 0.10 mol of N₂O₄(g) at 25°C. The gas dissociates according to the equilibrium:
N₂O₄(g) ⇌ 2NO₂(g)
At equilibrium, it is found that 0.04 mol of NO₂ is present.
(a) Calculate the number of moles of N₂O₄ remaining at equilibrium.
(b) Calculate the equilibrium concentrations of both N₂O₄ and NO₂.
(c) Explain why this equilibrium is called a homogeneous equilibrium.
Q17. In a school laboratory, a student sets up the following equilibrium in a closed flask at a constant temperature:
CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)
Initially, 0.20 mol of CO and 0.20 mol of H₂O are placed in a 1.0 L flask. At equilibrium, 0.08 mol of CO₂ is found.
(a) Set up an ICE table for this equilibrium.
(b) Calculate the equilibrium concentrations of all species.
(c) What does the value of the equilibrium constant tell you about the extent of this reaction?
Q18. Consider the following physical equilibria from daily life in India:
(a) A closed bottle of aerated water (soda) at room temperature contains CO₂ gas dissolved in water under pressure: CO₂(g) ⇌ CO₂(aq)
(i) What happens when the bottle is opened? Explain in terms of equilibrium shift.
(ii) Why do manufacturers keep soda bottles under high pressure?
(b) During summer, water kept in an earthen pot (matka) remains cooler than water in a metal container.
(i) Explain this observation using the concept of physical equilibrium between liquid water and water vapour.
(ii) How does the porous nature of the earthen pot help maintain this equilibrium?
(c) A student places a wet cloth over a water bottle to keep the water cool on a hot day. Explain the scientific principle behind this practice using equilibrium concepts.