Q. For a reaction with a rate constant of 0.5 s^-1, how long will it take for the concentration of a reactant to decrease to 25% of its initial value in a first-order reaction?
A.
1.386 seconds
B.
2 seconds
C.
4 seconds
D.
8 seconds
Solution
For a first-order reaction, the time to reach 25% of the initial concentration is t = (ln(1/0.25))/k = (ln(4))/0.5 = 2.772/0.5 = 5.544 seconds.
Q. For a reaction with an activation energy of 50 kJ/mol, what is the effect of increasing the temperature from 300 K to 350 K on the rate constant?
A.
Rate constant decreases
B.
Rate constant remains the same
C.
Rate constant increases
D.
Rate constant doubles
Solution
According to the Arrhenius equation, an increase in temperature generally increases the rate constant due to the exponential dependence on temperature.
Q. If the activation energy of a reaction is 50 kJ/mol, what is the effect of increasing the temperature from 300 K to 350 K on the rate constant?
A.
Rate constant decreases
B.
Rate constant remains the same
C.
Rate constant increases
D.
Rate constant doubles
Solution
According to the Arrhenius equation, an increase in temperature generally increases the rate constant, as it provides more energy to overcome the activation energy barrier.
Q. If the rate of a reaction is tripled when the concentration of reactant A is doubled, what is the order of the reaction with respect to A?
A.
0
B.
1
C.
2
D.
3
Solution
If tripling the rate occurs when doubling the concentration, the reaction is first order with respect to A, as rate ∝ [A]^n implies 3 = 2^n, leading to n = 1.
Q. What is the relationship between the rate constant and temperature for a reaction according to the Arrhenius equation?
A.
k = Ae^(-Ea/RT)
B.
k = Ea/RT
C.
k = RTe^(-Ea)
D.
k = A + Ea/RT
Solution
The Arrhenius equation states that the rate constant k is related to temperature T and activation energy Ea by k = Ae^(-Ea/RT), where A is the pre-exponential factor.
