Chemistry Multiple Choice Questions on “Chemical Kinetics – Integrated Rate Equations ”.
1. The rate constant of a reaction is 0.01s-1, how much time does it take for 2.4 mol L-1 concentration of reactant reduced to 0.3 mol L-1?
a) 108.3s-1
b) 207.9s-1
c) 248.2s-1
d) 164.8s-1
Answer: b
Clarification: Given,
K = 0.01s-1
t1/2 = 0.693/0.01
t1/2 = 69.3s
[R] = [R]0/2n
2n = [R]0/[R]
2n = 2.4/0.3
2n = 8
n = 3 (number of half-lives)
For 1 half-life t1/2 = 69.3s
For 3 half-life 3t1/2 = 3 x 69.3s = 207.9s.
2. What time does it take for reactants to reduce to 3/4 of initial concentration if the rate constant is 7.5 x 10-3 s-1?
a) 38.4s
b) 40.2s
c) 39.3s
d) 36.8s
Answer: a
Clarification: Given,
K=7.5 x 10-3 s-1
K = (2.303/t) x log([R]0/[R])
t = (2.303/7.5 x 10-3) x log([100]/[25])
t = (2.303/7.5 x 10-3) x 0.6
t = 38.4s.
3. A zero-order reaction is 25% complete in 30seconds. What time does it take for 50% completion?
a) 40s
b) 70s
c) 50s
d) 60s
Answer: d
Clarification:
t25% = (1-0.75)/K
K = 0.25/30
t50% = (1 x 30)/(2 x 0.25)
t50% = 15/0.25
t50% = 60s.
4. What is the integrated rate equation for a first order reaction?
a) [A] = [A]0e-kt
b) [A] = [A]0/e-kt
c) [A] = [A]0e-t
d) [A] = [A]0e-k
Answer: a
Clarification: A reaction is said to be of the first order if the rate of the reaction depends upon one concentration term only. The integrated rate equation for a first order reaction in exponential form is [A] = [A]0e-kt.
5. For a certain reaction the values of Arrhenius factor and Activation energy are 4 x 1013 collision/sec and 98.6KJ/mol at 303K. Calculate the rate constant if reaction is 1st order?( R=8.341mol-1K-1)
a) 6.07 x 10-3
b) 3.02 x 10-5
c) 4.07 x 10-4
d) 7.42 x 10-3
Answer: c
Clarification: Given,
Arrhenius factor(A) = 4 x 1013 collisions/sec
Activation energy (Ea)=98.6KJ/mol=98.6 x 103J/mol, T=303 K
log K = log A – (Ea/2.303RT)
log K = log (4 x 1013) – (98.6 x 103)/(2.303 x 8.314 x 303)
log K = 13.6020 – (98.6 x 103/5801.584)
log k = -3.39
K = 10-3.39
K = 4.07 x 10-4.
6. The decomposition of N2O5 in CCl4 solution was studied. N2O5 → 2NO2 + 1/2O2. The rate constant of the reaction is 6.2 x 10-4 sec-1. Calculate the rate when the concentration of N2O5 is 1.25 molar.
a) 6.45 x 10-4
b) 7.45 x 10-4
c) 6.75 x 10-4
d) 7.75 x 10-4
View Answer
Answer: d
Clarification: Given,
N2O5 → 2N02 + 1/2 O2
Rate = k[N2O5] 1
Rate =6.25 x 10-4 x [1.25]
Rate = 7.75 x 10-4.
7. What is the formula to calculate the time taken for the completion of a zero-order reaction?
a) t100% = [A]0/k
b) t100% = [A]0/2k
c) t100% = 2[A]0/k
d) t100% = [A]0/3k
Answer: a
Clarification: The time taken for the zero-order reaction to complete can be calculated as follows:
When the reaction is complete, [A]0 = 0
Therefore, k = [A]0/t or t100% = [A]0/k.
8. The unit of rate constant of a first-order reaction is s-1.
a) True
b) False
View Answer
Answer: a
Clarification: The rate constant is defined as the proportionality constant which explains the relationship between the molar concentration of the reactants and the rate of a chemical reaction. It is denoted by k.
For a first-order reaction, the unit of k is s-1.
9. The unit of the rate constant of a zero-order reaction and second-order reaction is same.
a) True
b) False