NEET Chemical Kinetics — Set 5

Question 1

A zero-order reaction has a rate constant of $ 6.0 \times 10^{-3} \, \text{mol L}^{-1} \text{min}^{-1} $. If the initial concentration is $ 0.18 \, \text{mol L}^{-1} $, how long will it take for 33.33% decomposition?

Accepted Answer

For zero-order, $ t = \frac{[\text{R}]_0 - [\text{R}]}{k} $. 33.33% decomposition means $ [\text{R}] = \frac{2}{3} \times 0.18 = 0.12 \, \text{mol L}^{-1} $. $ t = \frac{0.18 - 0.12}{6.0 \times 10^{-3}} = \frac{0.06}{6.0 \times 10^{-3}} = 10 \, \text{min} $.

Question 2

A second-order reaction has a rate constant of $ 0.2 \, \text{L mol}^{-1} \text{min}^{-1} $ and an initial concentration of $ 0.1 \, \text{mol L}^{-1} $. What is the time for 75% completion?

Accepted Answer

For second-order, $ \frac{1}{[\text{A}]} - \frac{1}{[\text{A}]_0} = kt $. 75% completion means $ [\text{A}] = 0.25 \times 0.1 = 0.025 \, \text{mol L}^{-1} $. $ \frac{1}{0.025} - \frac{1}{0.1} = 0.2 \times t $, $ 40 - 10 = 0.2 t $, $ t = \frac{30}{0.2} = 150 \, \text{min} $.

Question 3

A first-order gaseous reaction has an initial pressure of 1.0 atm. After 50 s, the total pressure is 1.5 atm. What is the rate constant?

Accepted Answer

For $ \text{A} \to 2\text{B} $, $ p_t = p_i + x $, $ x = 1.5 - 1.0 = 0.5 \, \text{atm} $. $ p_A = p_i - x = 1.0 - 0.5 = 0.5 \, \text{atm} $. $ k = \frac{2.303}{50} \log \frac{1.0}{0.5} = \frac{2.303 \times 0.301}{50} \approx 0.0139 \, \text{s}^{-1} $.

NEET Chemistry: Chemical Kinetics — Practice Set 5

Q1. A zero-order reaction has a rate constant of \( 6.0 \times 10^{-3} \, \text{mol L}^{-1} \text{min}^{-1} \). If the initial concentration is \( 0.18 \, \text{mol L}^{-1} \), how long will it take for 33.33% decomposition?

Q2. A second-order reaction has a rate constant of \( 0.2 \, \text{L mol}^{-1} \text{min}^{-1} \) and an initial concentration of \( 0.1 \, \text{mol L}^{-1} \). What is the time for 75% completion?

Q3. A first-order gaseous reaction has an initial pressure of 1.0 atm. After 50 s, the total pressure is 1.5 atm. What is the rate constant?

Q4. A reaction’s rate increases by 25 times when the concentration of the reactant is increased by 5 times. What is the order of the reaction?

Q5. A reaction has the rate law \( \text{Rate} = k[\text{A}]^{1.5}[\text{B}] \). What is the overall order?

Q6. A second-order reaction has a half-life of 60 s when the initial concentration is \( 0.1 \, \text{mol L}^{-1} \). What is the rate constant?

Q7. A second-order reaction has a rate constant of \( 0.05 \, \text{L mol}^{-1} \text{s}^{-1} \) and an initial concentration of \( 0.4 \, \text{mol L}^{-1} \). What is the time for 50% completion?

Q8. A reaction has the rate law \( \text{Rate} = k[\text{A}][\text{B}]^2 \). If the concentration of A is doubled and B is halved, what happens to the rate?

Q9. A second-order reaction has a rate constant of \( 0.07 \, \text{L mol}^{-1} \text{s}^{-1} \) and an initial concentration of \( 0.25 \, \text{mol L}^{-1} \). What is the time for 80% completion?

Q10. A second-order reaction has a half-life of 40 s when the initial concentration is \( 0.1 \, \text{mol L}^{-1} \). What is the rate constant?