NEET Chemical Kinetics — Set 19

Question 1

The molecularity of the elementary step $ \text{H}_2 + \text{Br}_2 \to 2\text{HBr} $ is:

Accepted Answer

Molecularity is the number of molecules in an elementary step. For $ \text{H}_2 + \text{Br}_2 $, two molecules collide, so molecularity = 2.

Question 2

The rate law for a reaction is $ \text{Rate} = k[\text{A}]^2[\text{B}] $. What is the overall order of the reaction?

Accepted Answer

Overall order = sum of the powers of concentration terms in the rate law. Given: $ \text{Rate} = k[\text{A}]^2[\text{B}]^1 $. Order = $ 2 + 1 = 3 $.

Question 3

A second-order reaction has a rate constant of $ 0.5 \, \text{L mol}^{-1} \text{min}^{-1} $. If the initial concentration is $ 0.2 \, \text{mol L}^{-1} $, what is the half-life?

Accepted Answer

For second-order, $ t_{1/2} = \frac{1}{k [\text{A}]_0} $. Given: $ k = 0.5 \, \text{L mol}^{-1} \text{min}^{-1} $, $ [\text{A}]_0 = 0.2 \, \text{mol L}^{-1} $. $ t_{1/2} = \frac{1}{0.5 \times 0.2} = \frac{1}{0.1} = 10 \, \text{min} $.

NEET Chemistry: Chemical Kinetics — Practice Set 19

Q1. The molecularity of the elementary step \( \text{H}_2 + \text{Br}_2 \to 2\text{HBr} \) is:

Q2. The rate law for a reaction is \( \text{Rate} = k[\text{A}]^2[\text{B}] \). What is the overall order of the reaction?

Q3. A second-order reaction has a rate constant of \( 0.5 \, \text{L mol}^{-1} \text{min}^{-1} \). If the initial concentration is \( 0.2 \, \text{mol L}^{-1} \), what is the half-life?

Q4. A reaction has the rate law \( \text{Rate} = k[\text{A}]^2[\text{B}]^{1/2} \). If the concentration of A is doubled and B is quadrupled, what happens to the rate?

Q5. For a first-order reaction, the time for 99% completion is approximately how many times the half-life?

Q6. A first-order reaction is 25% complete in 10 minutes. What is the rate constant?

Q7. The rate constant of a reaction doubles when the temperature increases from 300 K to 310 K. What is the approximate activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q8. A second-order reaction has a rate constant of \( 0.04 \, \text{L mol}^{-1} \text{min}^{-1} \) and an initial concentration of \( 0.25 \, \text{mol L}^{-1} \). What is the half-life?

Q9. A reaction has the rate law \( \text{Rate} = k[\text{A}][\text{B}]^{1/2} \). If the concentration of A is doubled and B is quadrupled, what happens to the rate?

Q10. The rate of a reaction triples when the concentration of the reactant is increased by 9 times. What is the order of the reaction?