NEET Chemical Kinetics — Set 18

Question 1

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

Accepted Answer

Initial rate = $ k [\text{A}] [\text{B}]^2 $. New rate = $ k \left( \frac{[\text{A}]}{2} \right) (3[\text{B}])^2 = k \times \frac{[\text{A}]}{2} \times 9 [\text{B}]^2 = \frac{9}{2} k [\text{A}] [\text{B}]^2 $. Rate increases by $ \frac{9}{2} = 4.5 $ times.

Question 2

A first-order reaction has a half-life of 18 minutes. What fraction of the reactant remains after 54 minutes?

Accepted Answer

Number of half-lives = $ \frac{54}{18} = 3 $. Fraction remaining = $ \left( \frac{1}{2} \right)^3 = \frac{1}{8} $.

Question 3

A reaction’s rate increases by 27 times when the concentration of the reactant is increased by 3 times. What is the order of the reaction?

Accepted Answer

Rate = $ k [\text{A}]^n $. New rate: $ k (3[\text{A}])^n = 27 k [\text{A}]^n $, so $ 3^n = 27 $. $ 3^n = 3^3 $, $ n = 3 $.

NEET Chemistry: Chemical Kinetics — Practice Set 18

Q1. A reaction has the rate law \( \text{Rate} = k[\text{A}][\text{B}]^2 \). If the concentration of A is halved and B is tripled, what happens to the rate?

Q2. A first-order reaction has a half-life of 18 minutes. What fraction of the reactant remains after 54 minutes?

Q3. A reaction’s rate increases by 27 times when the concentration of the reactant is increased by 3 times. What is the order of the reaction?

Q4. The decomposition of a gas follows first-order kinetics with an initial pressure of 0.8 atm. After 100 s, the total pressure is 1.2 atm. What is the rate constant?

Q5. The decomposition of a gas follows first-order kinetics with an initial pressure of 2.0 atm. After 60 s, the total pressure is 2.8 atm. What is the rate constant?

Q6. A reaction has the rate law \( \text{Rate} = k[\text{A}]^2[\text{B}] \). If the concentration of A is doubled and B is tripled, what happens to the rate?

Q7. The molecularity of the elementary step \( 2\text{NO} + \text{O}_2 \to 2\text{NO}_2 \) is:

Q8. A reaction has the rate law \( \text{Rate} = k[\text{A}]^2 \). If the concentration of A is tripled, by how many times will the rate increase?

Q9. A first-order gaseous reaction has an initial pressure of 1.2 atm. After 50 s, the total pressure is 1.6 atm. What is the rate constant?