NEET Chemical Kinetics — Set 7

Question 1

A second-order reaction has a rate constant of $ 0.08 \, \text{L mol}^{-1} \text{s}^{-1} $ and an initial concentration of $ 0.5 \, \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 0.5 = 0.125 \, \text{mol L}^{-1} $. $ \frac{1}{0.125} - \frac{1}{0.5} = 0.08 \times t $, $ 8 - 2 = 0.08 t $, $ t = \frac{6}{0.08} = 75 \, \text{s} $.

Question 2

A zero-order reaction has an initial concentration of $ 0.12 \, \text{mol L}^{-1} $ and a rate constant of $ 2.0 \times 10^{-3} \, \text{mol L}^{-1} \text{s}^{-1} $. What is the half-life?

Accepted Answer

For zero-order, $ t_{1/2} = \frac{[\text{R}]_0}{2k} $. Given: $ [\text{R}]_0 = 0.12 \, \text{mol L}^{-1} $, $ k = 2.0 \times 10^{-3} \, \text{mol L}^{-1} \text{s}^{-1} $. $ t_{1/2} = \frac{0.12}{2 \times 2.0 \times 10^{-3}} = \frac{0.12}{4.0 \times 10^{-3}} = 30 \, \text{s} $.

Question 3

The molecularity of the elementary step $ \text{NO} + \text{O}_3 \to \text{NO}_2 + \text{O}_2 $ is:

Accepted Answer

Molecularity is the number of molecules in an elementary step. For $ \text{NO} + \text{O}_3 $, two molecules collide, so molecularity = 2.

NEET Chemistry: Chemical Kinetics — Practice Set 7

Q1. A second-order reaction has a rate constant of \( 0.08 \, \text{L mol}^{-1} \text{s}^{-1} \) and an initial concentration of \( 0.5 \, \text{mol L}^{-1} \). What is the time for 75% completion?

Q2. A zero-order reaction has an initial concentration of \( 0.12 \, \text{mol L}^{-1} \) and a rate constant of \( 2.0 \times 10^{-3} \, \text{mol L}^{-1} \text{s}^{-1} \). What is the half-life?

Q3. The molecularity of the elementary step \( \text{NO} + \text{O}_3 \to \text{NO}_2 + \text{O}_2 \) is:

Q4. A first-order gaseous reaction has an initial pressure of 1.5 atm. After 25 s, the total pressure is 2.0 atm. What is the rate constant?

Q5. A first-order reaction is 10% complete in 5 minutes. What is the rate constant?

Q6. A first-order reaction has a rate constant of \( 0.0289 \, \text{min}^{-1} \). What is the time for 50% completion?

Q7. A first-order reaction has a half-life of 16 minutes. What percentage of the reactant decomposes in 48 minutes?

Q8. A zero-order reaction has a rate constant of \( 5.0 \times 10^{-4} \, \text{mol L}^{-1} \text{s}^{-1} \). If the initial concentration is \( 0.2 \, \text{mol L}^{-1} \), how long will it take for 20% decomposition?

Q9. A reaction’s rate constant increases from \( 4.0 \times 10^{-4} \, \text{s}^{-1} \) at 280 K to \( 1.2 \times 10^{-3} \, \text{s}^{-1} \) at 290 K. What is the activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q10. A first-order reaction has a rate constant of \( 0.0173 \, \text{min}^{-1} \). What percentage of the reactant decomposes in 80 minutes?