NEET Chemical Kinetics — Set 1

Question 1

The molecularity of the elementary step $ \text{N}_2\text{O}_5 \to \text{N}_2\text{O}_4 + \frac{1}{2}\text{O}_2 $ is:

Accepted Answer

Molecularity is the number of molecules in an elementary step. For $ \text{N}_2\text{O}_5 $, one molecule decomposes, so molecularity = 1.

Question 2

A first-order reaction has a rate constant of $ 0.0115 \, \text{min}^{-1} $. What is the time for 70% completion?

Accepted Answer

70% completion means 30% remains, $ \frac{[\text{R}]}{[\text{R}]_0} = 0.3 $, $ \frac{[\text{R}]_0}{[\text{R}]} = \frac{1}{0.3} \approx 3.333 $. $ t = \frac{2.303}{0.0115} \log 3.333 = \frac{2.303 \times 0.523}{0.0115} \approx 105 \, \text{min} $.

Question 3

A reaction’s rate increases by 2.83 times when the temperature rises from 320 K to 330 K. What is the activation energy ($ R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} $)?

Accepted Answer

$ \log \frac{k_2}{k_1} = \frac{E_a}{2.303 R} \left( \frac{T_2 - T_1}{T_1 T_2} \right) $. $ \log 2.83 \approx 0.452 $, $ E_a = \frac{0.452 \times 19.147 \times 105600}{10} \approx 91,400 \, \text{J mol}^{-1} \approx 91.4 \, \text{kJ mol}^{-1} $.

NEET Chemistry: Chemical Kinetics — Practice Set 1

Q1. The molecularity of the elementary step \( \text{N}_2\text{O}_5 \to \text{N}_2\text{O}_4 + \frac{1}{2}\text{O}_2 \) is:

Q2. A first-order reaction has a rate constant of \( 0.0115 \, \text{min}^{-1} \). What is the time for 70% completion?

Q3. A reaction’s rate increases by 2.83 times when the temperature rises from 320 K to 330 K. What is the activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q4. A first-order gaseous reaction has an initial pressure of 2.0 atm. After 20 s, the total pressure is 2.5 atm. What is the rate constant?

Q5. A first-order reaction has a half-life of 25 minutes. What fraction of the reactant remains after 50 minutes?

Q6. A reaction’s rate increases by 8 times when the concentration of the reactant is increased by 2 times. What is the order of the reaction?

Q7. A second-order reaction has a rate constant of \( 0.05 \, \text{L mol}^{-1} \text{s}^{-1} \) and an initial concentration of \( 0.1 \, \text{mol L}^{-1} \). What is the half-life?

Q8. A first-order reaction has a rate constant of \( 0.0231 \, \text{min}^{-1} \). What is the half-life?

Q9. A first-order reaction has a rate constant of \( 0.0346 \, \text{min}^{-1} \). What percentage of the reactant decomposes in 40 minutes?

Q10. For the reaction \( \text{A} + \text{B} \to 2\text{C} \), the rate of formation of C is \( 0.06 \, \text{mol L}^{-1} \text{min}^{-1} \). What is the rate of disappearance of A?