Q. 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)
A.25 s
B.50 s
C.10 s
D.20 s
Solution
Using t = 1 / (k[A₀]) * (1/[A] - 1/[A₀]), t = 1 / (0.02 * 0.5) * (1/0.25 - 1/0.5) = 25 s.
Q. If the rate of a reaction is directly proportional to the concentration of one reactant raised to the power of 3, what is the order of the reaction? (2023)
A.Zero
B.First
C.Second
D.Third
Solution
The order of the reaction is third because the rate is proportional to the concentration raised to the power of 3.
Q. In a reaction, if the concentration of reactant A is halved, and the rate constant remains the same, how does the rate change for a first-order reaction? (2021)
A.Doubles
B.Halves
C.Remains the same
D.Quadruples
Solution
For a first-order reaction, if [A] is halved, the rate also halves.
Q. In a reaction, if the concentration of reactant A is halved, and the rate of reaction decreases to one-fourth, what is the order of the reaction? (2020)
A.Zero
B.First
C.Second
D.Third
Solution
If the rate decreases to one-fourth when concentration is halved, the reaction is second-order.
Q. 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)
A.10 s
B.20 s
C.5 s
D.15 s
Solution
For a second-order reaction, t₁/₂ = 1 / (k[A₀]) = 1 / (0.05 * 0.1) = 200 s.
Q. 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)
A.mol/L·s
B.L^2/mol·s
C.mol/L
D.s^-1
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.
Q. The half-life of a first-order reaction is independent of the initial concentration of the reactant. What is the formula for the half-life (t1/2) of a first-order reaction? (2020)
A.t1/2 = 0.693/k
B.t1/2 = k/0.693
C.t1/2 = 1/k
D.t1/2 = k/1
Solution
The half-life of a first-order reaction is given by the formula t1/2 = 0.693/k, where k is the rate constant.
Q. What is the rate law expression for a reaction that is first order with respect to A and second order with respect to B? (2022)
A.Rate = k[A][B]^2
B.Rate = k[A]^2[B]
C.Rate = k[A]^2[B]^2
D.Rate = k[A][B]
Solution
The rate law for a reaction is determined by the order with respect to each reactant. For a first order with respect to A and second order with respect to B, the rate law is Rate = k[A][B]^2.
Q. 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
A.Rate = k[A][B]^2
B.Rate = k[A]^2[B]
C.Rate = k[A]^2[B]^2
D.Rate = k[A][B]
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.
