Factors Affecting Rate - UNSOLVED PRACTICE SET
Chapter: Chemical Kinetics | Topic: Factors Affecting Rate
FACTORS AFFECTING RATE - UNSOLVED PRACTICE SET
Topic: Factors Affecting Rate
Multiple Choice Questions
1. Which of the following factors does NOT affect the rate of a chemical reaction?
- Concentration of reactants
- Colour of the reactants
- Temperature
- Presence of a catalyst
2. Increasing the concentration of reactants increases the rate of reaction because:
- It decreases the activation energy
- It increases the number of collisions per unit time
- It changes the nature of the reaction
- It decreases the temperature of the system
3. The rate of reaction approximately doubles or triples for every:
- 1°C rise in temperature
- 5°C rise in temperature
- 10°C rise in temperature
- 50°C rise in temperature
4. A catalyst increases the rate of reaction by:
- Increasing the activation energy
- Providing an alternative pathway with lower activation energy
- Increasing the enthalpy change of the reaction
- Decreasing the concentration of reactants
5. The surface area of reactants affects the rate of reaction because:
- It changes the chemical nature of the reactants
- More surface area exposes more particles for collision
- It increases the temperature automatically
- It decreases the number of effective collisions
6. In a gaseous reaction, increasing the pressure (at constant temperature) increases the rate because:
- It increases the kinetic energy of molecules
- It increases the concentration of gaseous reactants
- It changes the activation energy
- It introduces a catalyst
Short Answer Questions
7. Why does powdered zinc react faster with dilute HCl than zinc granules of the same mass?
8. Explain why food kept in a refrigerator stays fresh for a longer time, using the concept of temperature and reaction rate.
9. A student is making chapatis. She notices that finely ground wheat flour makes softer chapatis faster than coarse flour. Which factor affecting reaction rate does this illustrate? Explain.
10. How does the nature of the reactants affect the rate of a chemical reaction? Give one example.
11. Why does a glowing splint burst into flames when introduced into a jar of pure oxygen, but only glows in air?
12. Explain the role of a catalyst with a suitable example from everyday life or an industrial process.
Long Answer Questions
13. Discuss the various factors that affect the rate of a chemical reaction. Explain each factor with a real-life or laboratory example.
14. (a) Why does increasing the temperature increase the rate of reaction? Explain in terms of collision theory.
(b) A reaction is carried out at 25°C and then at 35°C. By approximately what factor would you expect the rate to increase? Explain.
15. In your school chemistry lab, you are given two samples of calcium carbonate—one as large marble chips and one as fine powder. You are asked to react both with dilute HCl separately.
(a) Which sample will react faster? Why?
(b) How would you compare the rates in the lab? What would you observe?
(c) Does the total amount of CO₂ produced differ between the two samples? Explain.
Numerical / Application-Based Problems
16. The rate of a certain reaction is studied at different temperatures. It is observed that the rate constant doubles when the temperature is increased from 300 K to 310 K.
(a) Calculate the approximate increase in rate when the temperature is raised from 300 K to 330 K.
(b) Explain why this happens using collision theory concepts.
17. A catalyst lowers the activation energy of a reaction from 75 kJ/mol to 45 kJ/mol. Using the Arrhenius equation concept (qualitative explanation only):
(a) Explain how this affects the rate constant.
(b) By what factor would you expect the rate to increase at a given temperature? (Assume all other factors remain constant.)
18. In an experiment to study the effect of concentration on reaction rate, a student mixes 50 mL of 0.1 M Na₂S₂O₃ with 10 mL of 1 M HCl and records the time for a cross placed under the flask to disappear. The experiment is repeated with 25 mL of 0.1 M Na₂S₂O₃ + 25 mL of water + 10 mL of 1 M HCl.
(a) In which case will the cross disappear faster? Why?
(b) What does this experiment demonstrate about the effect of concentration on reaction rate?
(c) Write the balanced chemical equation for this reaction.