Chapter 4: Chemical Kinetics

NCERT Solutions for CBSE Class 10 Chemistry — 35 solved questions with detailed explanations.

Questions

Topics

Solved Questions

Q1. The half-life of a first-order reaction is:

k/0.693
0.693/k
2.303/k
k/2.303

Difficulty: Easy · Topic: First Order

Solution

t½ = 0.693/k = ln2/k for first-order reactions. Independent of initial concentration.

Q2. The rate constant of a reaction increases with temperature because:

Collision frequency doubles
Activation energy decreases
Fraction of molecules with E ≥ E_a increases
Equilibrium shifts

Difficulty: Easy-Medium · Topic: Arrhenius Equation

Solution

Arrhenius equation: k = Ae^(-Ea/RT). Higher T → more molecules exceed activation energy barrier.

Q3. For a zero-order reaction, the plot of [A] vs time is:

Exponential
Straight line with negative slope
Straight line with positive slope
Parabola

Difficulty: Easy-Medium · Topic: Zero Order

Solution

Zero order: [A] = [A]₀ - kt. Linear decrease with time, slope = -k.

Q4. The units of rate constant for a second-order reaction are:

s⁻¹
mol⁻¹ L s⁻¹
mol L⁻¹ s⁻¹
mol⁻² L² s⁻¹

Difficulty: Easy-Medium · Topic: Rate Constant Units

Solution

Rate = k[A]². k = Rate/[A]² = (mol L⁻¹ s⁻¹)/(mol² L⁻²) = mol⁻¹ L s⁻¹ = L mol⁻¹ s⁻¹.

Q5. For a first-order reaction with k = 0.001 s⁻¹, the half-life is:

Difficulty: Easy-Medium · Topic: First Order Kinetics

Solution

t½ = 0.693/k = 0.693/0.001 = 693.0 s.

Q6. For a first-order reaction with k = 0.01 s⁻¹, the half-life is:

Difficulty: Easy-Medium · Topic: First Order Kinetics

Solution

t½ = 0.693/k = 0.693/0.01 = 69.3 s.

Q7. For a first-order reaction with k = 0.1 s⁻¹, the half-life is:

Difficulty: Easy-Medium · Topic: First Order Kinetics

Solution

t½ = 0.693/k = 0.693/0.1 = 6.93 s.

Q8. For a first-order reaction with k = 0.05 s⁻¹, the half-life is:

Difficulty: Easy-Medium · Topic: First Order Kinetics

Solution

t½ = 0.693/k = 0.693/0.05 = 13.86 s.

Q9. For a first-order reaction with k = 0.02 s⁻¹, the half-life is:

Difficulty: Easy-Medium · Topic: First Order Kinetics

Solution

t½ = 0.693/k = 0.693/0.02 = 34.65 s.

Q10. For a first-order reaction with k = 0.005 s⁻¹, the half-life is:

Difficulty: Easy-Medium · Topic: First Order Kinetics

Solution

t½ = 0.693/k = 0.693/0.005 = 138.6 s.

Q11. First-order reaction with k=0.001 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.001 = 693.0 s.

Q12. First-order reaction with k=0.002 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.002 = 346.5 s.

Q13. First-order reaction with k=0.005 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.005 = 138.6 s.

Q14. First-order reaction with k=0.01 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.01 = 69.3 s.

Q15. First-order reaction with k=0.02 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.02 = 34.65 s.

Q16. First-order reaction with k=0.05 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.05 = 13.86 s.

Q17. First-order reaction with k=0.1 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.1 = 6.93 s.

Q18. First-order reaction with k=0.2 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.2 = 3.465 s.

Q19. First-order reaction with k=0.5 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life

Solution

t½ = 0.693/0.5 = 1.386 s.

Q20. First-order reaction with k=1.0 s⁻¹ has half-life:

Difficulty: Easy-Medium · Topic: Half-life