NEET Chemical Kinetics — Set 6

Question 1

A first-order gaseous reaction has an initial pressure of 1.2 atm. After 30 s, the total pressure is 1.8 atm. What is the rate constant?

Accepted Answer

For $ \text{A} \to 2\text{B} $, $ p_t = p_i + x $, $ x = 1.8 - 1.2 = 0.6 \, \text{atm} $. $ p_A = p_i - x = 1.2 - 0.6 = 0.6 \, \text{atm} $. $ k = \frac{2.303}{30} \log \frac{1.2}{0.6} = \frac{2.303 \times 0.301}{30} \approx 0.0231 \, \text{s}^{-1} $.

Question 2

A zero-order reaction has a rate constant of $ 6.0 \times 10^{-4} \, \text{mol L}^{-1} \text{s}^{-1} $. If the initial concentration is $ 0.09 \, \text{mol L}^{-1} $, how long will it take for 66.67% decomposition?

Accepted Answer

For zero-order, $ k = \frac{[\text{R}]_0 - [\text{R}]}{t} $. 66.67% decomposition means $ [\text{R}] = \frac{1}{3} \times 0.09 = 0.03 \, \text{mol L}^{-1} $. $ t = \frac{0.09 - 0.03}{6.0 \times 10^{-4}} = \frac{0.06}{6.0 \times 10^{-4}} = 100 \, \text{s} $.

Question 3

A first-order reaction has a rate constant of $ 0.01386 \, \text{min}^{-1} $. What is its half-life?

Accepted Answer

For a first-order reaction, $ t_{1/2} = \frac{0.693}{k} $. Given: $ k = 0.01386 \, \text{min}^{-1} $. $ t_{1/2} = \frac{0.693}{0.01386} \approx 50 \, \text{min} $.

NEET Chemistry: Chemical Kinetics — Practice Set 6

Q1. A first-order gaseous reaction has an initial pressure of 1.2 atm. After 30 s, the total pressure is 1.8 atm. What is the rate constant?

Q2. A zero-order reaction has a rate constant of \( 6.0 \times 10^{-4} \, \text{mol L}^{-1} \text{s}^{-1} \). If the initial concentration is \( 0.09 \, \text{mol L}^{-1} \), how long will it take for 66.67% decomposition?

Q3. A first-order reaction has a rate constant of \( 0.01386 \, \text{min}^{-1} \). What is its half-life?

Q4. A zero-order reaction has an initial concentration of \( 0.27 \, \text{mol L}^{-1} \) and a rate constant of \( 4.5 \times 10^{-3} \, \text{mol L}^{-1} \text{s}^{-1} \). What is the half-life?

Q5. A second-order reaction has a rate constant of \( 0.05 \, \text{L mol}^{-1} \text{min}^{-1} \) and an initial concentration of \( 0.4 \, \text{mol L}^{-1} \). What is the time for 80% completion?

Q6. A reaction’s rate increases by 1.73 times when the temperature rises from 290 K to 300 K. What is the activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q7. A first-order reaction has a half-life of 25 minutes. What percentage of the reactant remains after 75 minutes?

Q8. For the reaction \( 2\text{A} + \text{B} \to 3\text{C} \), the rate of disappearance of B is \( 0.03 \, \text{mol L}^{-1} \text{min}^{-1} \). What is the rate of formation of C?

Q9. The rate of a reaction increases by 27 times when the concentration of the reactant is increased by 3 times. What is the order of the reaction?

Q10. The molecularity of the reaction \( 2\text{NO} + \text{O}_2 \to 2\text{NO}_2 \) is: