NEET Chemical Kinetics — Set 2

Question 1

A first-order reaction is 20% complete in 10 minutes. What is the rate constant?

Accepted Answer

For first-order, $ k = \frac{2.303}{t} \log \frac{[\text{R}]_0}{[\text{R}]} $. 20% complete means 80% remains, $ \frac{[\text{R}]}{[\text{R}]_0} = 0.8 $, $ \frac{[\text{R}]_0}{[\text{R}]} = 1.25 $. $ k = \frac{2.303}{10} \log 1.25 = \frac{2.303 \times 0.0969}{10} \approx 0.0223 \, \text{min}^{-1} $.

Question 2

A reaction has the rate law $ \text{Rate} = k[\text{A}]^2[\text{B}] $. If the concentration of A is tripled and B is doubled, by how many times will the rate increase?

Accepted Answer

Initial rate = $ k [\text{A}]^2 [\text{B}] $. New rate = $ k (3[\text{A}])^2 (2[\text{B}]) = k \times 9 [\text{A}]^2 \times 2 [\text{B}] = 18 k [\text{A}]^2 [\text{B}] $. Rate increases by 18 times.

Question 3

A reaction has a rate constant of $ 0.05 \, \text{L mol}^{-1} \text{s}^{-1} $. What is its order?

Accepted Answer

For a second-order reaction, the unit of $ k $ is $ \text{L mol}^{-1} \text{s}^{-1} $. Given: $ k = 0.05 \, \text{L mol}^{-1} \text{s}^{-1} $, which matches the unit for a second-order reaction. Thus, the order is 2.

NEET Chemistry: Chemical Kinetics — Practice Set 2

Q1. A first-order reaction is 20% complete in 10 minutes. What is the rate constant?

Q2. A reaction has the rate law \( \text{Rate} = k[\text{A}]^2[\text{B}] \). If the concentration of A is tripled and B is doubled, by how many times will the rate increase?

Q3. A reaction has a rate constant of \( 0.05 \, \text{L mol}^{-1} \text{s}^{-1} \). What is its order?

Q4. A reaction’s rate increases by 2.25 times when the concentration of the reactant is increased by 1.5 times. What is the order of the reaction?

Q5. A reaction has the rate law \( \text{Rate} = k[\text{A}]^2 \). If the concentration of A is increased by 5 times, by how many times will the rate increase?

Q6. A second-order reaction has a rate constant of \( 0.02 \, \text{L mol}^{-1} \text{s}^{-1} \) and an initial concentration of \( 0.2 \, \text{mol L}^{-1} \). What is the half-life?

Q7. A first-order reaction has a rate constant of \( 0.0115 \, \text{min}^{-1} \). What percentage of the reactant remains after 60 minutes?

Q8. For a reaction \( \text{A} + 2\text{B} \to \text{C} \), the rate of disappearance of B is \( 0.06 \, \text{mol L}^{-1} \text{s}^{-1} \). What is the rate of reaction?

Q9. A zero-order reaction has an initial concentration of \( 0.15 \, \text{mol L}^{-1} \) and a rate constant of \( 2.5 \times 10^{-3} \, \text{mol L}^{-1} \text{s}^{-1} \). What is the half-life?

Q10. The half-life of a first-order reaction is 20 minutes. What is the rate constant?