CHEMICAL KINETICS QUIZ-2

Q1. For the reaction, 2N_2 O_5 (g)→4NO_2 (g)+O_2 (g) If the concentration of NO_2 increase by 5.2×〖10〗^(-3) M in 100 s then the rate of the reactions

•  2×〖10〗^(-3) Ms^(-1)
•  7.6×〖10〗^(-4) Ms^(-1)
•  0.5×〖10〗^(-4) Ms^(-1)
•  1.3×〖10〗^(-5) Ms^(-1)

Solution
Rate of reaction =1/4 d(NO_2 )/dt=(5.2×〖10〗^(-3))/(4×100) =1.3×〖10〗^(-5 ) Ms^(-1)

Q2.For a fist order reaction, the concentration changes from 0.8 to 0.4 in 15 min. The time taken for the concentration to change from 0.1 M to 0.025 M is

•  60 min
•  30 Min
•  15 Min
•  7.5 min

Solution
T_50=15 min k=2.303log2/T_50 =2.303log2/15 a=0.1M (a-x)=0.025 M For first order reaction, k=2.303log2/T_50 log⁡(a/(a-x)) 2.303log2/15=(2×2.303log2)/t log 0.1/0.025 =2.303/t log4 ∴2.303log2/15=(2×2.303log2)/t ∴ t=30 min

Q3.  If the concentration units are reduced by n times, then the value of rate constant of first order will:

•   Increase by n times
•  Decrease by factor of n
•  None of these
•  Not change

Solution
Rate constant is characteristic constant of a reaction and depends only on temperature and catalyst.

Q4. Inversion of cane-sugar in dilute acid is a

•  Bimolecular reaction
•  Trimolecular reaction
•  Unimolecular reaction
•  Pseudo-unimolecular reaction

Solution
c_12 H_22 O_11+H_2 O□(→┴(Dil.acid) ) C_6 H_12 O_6+C_6+H_12 O_6 Excess glucose fructose when one of the reactant is present in large excess, the second order reaction confirms to the first order and is knows as Pseudo-unimolecular reaction

Q5.The unit of rate constant for a zero order reaction

•  mol L^(-1) s^(-1)
•  mol s^(-1)
•  L s^(-1)
•  L mol^(-1) s^(-1)

Solution
 C

Q6. For the reaction; 2N_2 O_5⟶4NO_2+O_2, rate and rate constant are 1.02×〖10〗^(-4) M sec^(-1)⁡and 3.4×〖10〗^(-5) sec^(-1)⁡M respectively, then concentration of N_2 O_5, at that time will be:

•  1.732 M
•  3 M
• 1.02×〖10〗^(-4) M
•  3.5×〖10〗^5 M

Solution
r=K[N_2 O_5] ∴[N_2 O_5 ]=r/K=(1.02×〖10〗^(-4))/(3.4×〖10〗^(-5) )=3M .

Q7.If “a” and “t_(1/2)” are initial concentration of reactant and half-life of a zero order reaction respectively, which of the following is correct ?

•  t_(1/2)∝a^2
•  t_(1/2)∝1/a^2
•  t_(1/2)∝a
•  t_(1/2)∝1/a

Solution
For zero order reaction integrated rate equation is kt=[A]_0-[A] If 〖[A]〗_0=a,[A]=a/2,t=t_(1/2) kt_(1/2)=a-a/2 kt_(1/2)=a/2 t_(1/2)=a/2k ∴ t_(1/2)∝a

Q8.In the reaction 2A+B→A_2 B, if the concentration of A is doubled and of B is halved, then the rate of the reaction will

•  Decrease by two times
•  Increase by two times
•  Increase by four times
•  Remain the same

Solution
2A+B→A_2 B r_1=k[A]^2 [B] r_2=k[2A]^2 [B/2] Or r_2=2k[A]^2 [B] ∴r_2=2r_1

Q9.The Arrhenius equation expressing the effect of temperature on the rate constant of reaction is:

•  K=E_a/RT
•  K=e^(-Ea/RT)
•  K=log_e⁡〖E_a/RT〗
•  K=Ae^(-E_a/RT)

Solution
This is Arrhenius equation.

Q10. The rate constant is given by the equation K=Ae^(-E_a/RT) which factor should register a decrease for the reaction to proceed more rapidly?

•  A
•  E_a
•  Z
• T

Solution
A decrease in E_a will increase rate constant K and thus rate of reaction increases.