NEET Chemical Kinetics — Set 15

Question 1

For the reaction $ \text{A} + 2\text{B} \to \text{C} + \text{D} $, the rate of formation of D is $ 0.04 \, \text{mol L}^{-1} \text{s}^{-1} $. What is the rate of disappearance of B?

Accepted Answer

Rate = $ -\frac{1}{2} \frac{\Delta[\text{B}]}{\Delta t} = \frac{\Delta[\text{D}]}{\Delta t} $. Given: $ \frac{\Delta[\text{D}]}{\Delta t} = 0.04 \, \text{mol L}^{-1} \text{s}^{-1} $. $ -\frac{\Delta[\text{B}]}{\Delta t} = 2 \times 0.04 = 0.08 \, \text{mol L}^{-1} \text{s}^{-1} $.

Question 2

A reaction’s rate constant increases from $ 2.5 \times 10^{-4} \, \text{s}^{-1} $ at 27°C to $ 7.5 \times 10^{-4} \, \text{s}^{-1} $ at 37°C. What is the activation energy ($ R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} $)?

Accepted Answer

$ T_1 = 300 \, \text{K} $, $ T_2 = 310 \, \text{K} $. $ \log \frac{7.5 \times 10^{-4}}{2.5 \times 10^{-4}} = \frac{E_a}{2.303 \times 8.314} \left( \frac{10}{300 \times 310} \right) $. $ \log 3 = 0.477 $, $ E_a = \frac{0.477 \times 19.147 \times 93000}{10} \approx 84,900 \, \text{J mol}^{-1} \approx 84.9 \, \text{kJ mol}^{-1} $.

Question 3

A zero-order reaction reduces the concentration from $ 0.18 \, \text{mol L}^{-1} $ to $ 0.09 \, \text{mol L}^{-1} $ in 45 s. What is the rate constant?

Accepted Answer

For zero-order, $ k = \frac{[\text{R}]_0 - [\text{R}]}{t} $. Given: $ [\text{R}]_0 = 0.18 \, \text{mol L}^{-1} $, $ [\text{R}] = 0.09 \, \text{mol L}^{-1} $, $ t = 45 \, \text{s} $. $ k = \frac{0.18 - 0.09}{45} = \frac{0.09}{45} = 2.0 \times 10^{-3} \, \text{mol L}^{-1} \text{s}^{-1} $.

NEET Chemistry: Chemical Kinetics — Practice Set 15

Q1. For the reaction \( \text{A} + 2\text{B} \to \text{C} + \text{D} \), the rate of formation of D is \( 0.04 \, \text{mol L}^{-1} \text{s}^{-1} \). What is the rate of disappearance of B?

Q2. A reaction’s rate constant increases from \( 2.5 \times 10^{-4} \, \text{s}^{-1} \) at 27°C to \( 7.5 \times 10^{-4} \, \text{s}^{-1} \) at 37°C. What is the activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q3. A zero-order reaction reduces the concentration from \( 0.18 \, \text{mol L}^{-1} \) to \( 0.09 \, \text{mol L}^{-1} \) in 45 s. What is the rate constant?

Q4. A zero-order reaction has a rate constant of \( 5.0 \times 10^{-3} \, \text{mol L}^{-1} \text{min}^{-1} \). If the initial concentration is \( 0.25 \, \text{mol L}^{-1} \), how long will it take for 60% decomposition?

Q5. For the reaction \( 3\text{A} + \text{B} \to 2\text{C} \), the rate of disappearance of A is \( 0.12 \, \text{mol L}^{-1} \text{s}^{-1} \). What is the rate of formation of C?

Q6. A reaction’s rate constant doubles when the temperature increases from 350 K to 360 K. What is the activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q7. The rate constant of a reaction is \( 5.0 \times 10^{-4} \, \text{s}^{-1} \) at 350 K and \( 2.0 \times 10^{-3} \, \text{s}^{-1} \) at 360 K. What is the activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?

Q8. A first-order gaseous reaction has an initial pressure of 0.8 atm. After 30 s, the total pressure is 1.0 atm. What is the rate constant?

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

Q10. A reaction’s rate increases by 2 times when the temperature rises from 25°C to 35°C. What is the activation energy (\( R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1} \))?