Q1. In a second-order reaction, if the initial concentration is 0.1 M and the rate constant is 0.05 M⁻¹s⁻¹, what is the time taken to reach half the initial concentration? (2020)
Solution:
For a second-order reaction, t₁/₂ = 1 / (k[A₀]) = 1 / (0.05 * 0.1) = 200 s.
⏱ Time: 0s
Q2. In a zero-order reaction, the rate of reaction is independent of which of the following? (2023) 2023
Solution:
In a zero-order reaction, the rate is constant and does not depend on the concentration of the reactants.
⏱ Time: 0s
Q3. In a zero-order reaction, the rate of reaction is independent of the concentration of the reactants. What is the unit of the rate constant (k) for a zero-order reaction? (2023)
Solution:
For a zero-order reaction, the rate is constant and does not depend on the concentration of reactants. The unit of the rate constant (k) is mol/L·s.
⏱ Time: 0s
Q4. In a first-order reaction, if the concentration of reactant decreases from 0.8 M to 0.2 M in 20 minutes, what is the rate constant? (2022)
Solution:
Using the first-order rate equation, k = (ln[A₀] - ln[A]) / t. Here, k = (ln(0.8) - ln(0.2)) / 20 = 0.0347 min⁻¹.
⏱ Time: 0s
Q5. In a first-order reaction, if the half-life is constant, what can be said about the rate constant? (2023)
Solution:
In a first-order reaction, the half-life is constant, which indicates that the rate constant remains constant.
⏱ Time: 0s
Q6. What is the rate constant of a first-order reaction if the half-life is 10 minutes? (2021)
Solution:
For a first-order reaction, k = 0.693 / t₁/₂. Here, t₁/₂ = 10 min, so k = 0.693 / 10 = 0.0693 min⁻¹.
⏱ Time: 0s
Q7. For a reaction with an activation energy of 50 kJ/mol, what is the rate constant at 300 K if R = 8.314 J/(mol·K)? (2022)
Solution:
Using the Arrhenius equation, k = Ae^(-Ea/RT). Calculate k using the given values.
⏱ Time: 0s
Q8. For a zero-order reaction, if the initial concentration is 0.5 M and the rate constant is 0.1 M/s, how long will it take to reach 0.2 M? (2021)
Solution:
For a zero-order reaction, t = [A₀ - A] / k. Here, t = (0.5 - 0.2) / 0.1 = 3 s.
⏱ Time: 0s
Q9. What is the rate law for a reaction that is first order with respect to A and second order with respect to B? (2022) 2022
Solution:
The rate law is determined by the order of the reaction with respect to each reactant. For first order in A and second order in B, the rate law is Rate = k[A][B]^2.
⏱ Time: 0s
Q10. For a reaction with a rate constant of 0.02 M⁻¹s⁻¹ and initial concentration of 0.5 M, what is the time taken to reach 0.25 M in a second-order reaction? (2023)
Solution:
Using t = 1 / (k[A₀]) * (1/[A] - 1/[A₀]), t = 1 / (0.02 * 0.5) * (1/0.25 - 1/0.5) = 25 s.
