NEET Chemical Kinetics — Set 20

Question 1

A reaction’s rate increases by 2.25 times when the temperature rises from 300 K to 310 K. What is the activation energy ($ R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} $)?

Accepted Answer

$ \log \frac{k_2}{k_1} = \frac{E_a}{2.303 R} \left( \frac{T_2 - T_1}{T_1 T_2} \right) $. $ \log 2.25 = 0.352 $, $ E_a = \frac{0.352 \times 19.147 \times 93000}{10} \approx 62,700 \, \text{J mol}^{-1} \approx 62.7 \, \text{kJ mol}^{-1} $.

Question 2

The rate constant of a reaction is $ 3.0 \times 10^{-3} \, \text{s}^{-1} $ at 27°C. If the activation energy is 55 kJ/mol, what is the rate constant at 37°C ($ R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} $)?

Accepted Answer

$ T_1 = 300 \, \text{K} $, $ T_2 = 310 \, \text{K} $. $ \log \frac{k_2}{3.0 \times 10^{-3}} = \frac{55000}{2.303 \times 8.314} \left( \frac{10}{300 \times 310} \right) \approx 0.309 $. $ \frac{k_2}{3.0 \times 10^{-3}} = 10^{0.309} \approx 2.04 $, $ k_2 \approx 6.12 \times 10^{-3} \, \text{s}^{-1} $.

Question 3

A second-order reaction has an initial concentration of $ 0.3 \, \text{mol L}^{-1} $ and a half-life of 20 s. What is the rate constant?

Accepted Answer

For second-order, $ t_{1/2} = \frac{1}{k [\text{A}]_0} $. Given: $ t_{1/2} = 20 \, \text{s} $, $ [\text{A}]_0 = 0.3 \, \text{mol L}^{-1} $. $ k = \frac{1}{20 \times 0.3} = \frac{1}{6} \approx 0.1667 \, \text{L mol}^{-1} \text{s}^{-1} $.

NEET Chemistry: Chemical Kinetics — Practice Set 20

Q1. A reaction’s rate increases by 2.25 times when the temperature rises from 300 K to 310 K. What is the activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q2. The rate constant of a reaction is \( 3.0 \times 10^{-3} \, \text{s}^{-1} \) at 27°C. If the activation energy is 55 kJ/mol, what is the rate constant at 37°C (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q3. A second-order reaction has an initial concentration of \( 0.3 \, \text{mol L}^{-1} \) and a half-life of 20 s. What is the rate constant?

Q4. The molecularity of the elementary step \( \text{Cl}_2 + \text{H}_2 \to 2\text{HCl} \) is:

Q5. A first-order reaction is 25% complete in 15 minutes. What is the rate constant?

Q6. A first-order reaction is 40% complete in 15 minutes. What is the rate constant?

Q7. A first-order reaction is 20% complete in 12 minutes. What is the rate constant?

Q8. A zero-order reaction has a rate constant of \( 2.0 \times 10^{-3} \, \text{mol L}^{-1} \text{s}^{-1} \). How long will it take for the concentration to decrease from \( 0.12 \, \text{mol L}^{-1} \) to \( 0.03 \, \text{mol L}^{-1} \)?

Q9. A first-order reaction has a half-life of 24 minutes. What percentage of the reactant remains after 72 minutes?

Q10. For the reaction \( \text{A} + 3\text{B} \to 2\text{C} \), the rate of disappearance of A is \( 0.02 \, \text{mol L}^{-1} \text{min}^{-1} \). What is the rate of formation of C?