Chemical Kinetics(12th Grade > Chemistry ) Questions and answers for exam Preparation

12th Grade > Chemistry

CHEMICAL KINETICS MCQs

Total Questions : 30 | Page 2 of 3 pages

Question 11. Milk turns sour at

40^{\circ}

C three times as faster as

0^{\circ}

C. Hence,

E_{a}

in the process of turning of milk sour is

2.303×2×313×27340log3
2.303×2×313×27340log(1/3) cal
2.303×2×40273×313log3 cal
None of these

Discuss Question

Answer: Option A. -> 2.303×2×313×27340log3
:
A

K_{40^{\circ} C} = A e^{- E a / R \times 313} K_{0^{\circ} C} = A e^{- E a / R \times 273} 3 = e^{- E a / R \times (1 / 313 - 1 / 273)}

On taking logs on both sides, you get the required answer

Question 12. Which one of the following is a second order reaction?

H2+Br2→2HBr
NH4NO3→N2+3H2O
H2+Cl2→2HCl
CH3COOCH3+NaOH→CH3COONa+CH3OH

Discuss Question

Answer: Option D. -> CH3COOCH3+NaOH→CH3COONa+CH3OH
:
D
Choices (a) and (c) are photochemical reaction of zero order. Choice (b) is first order reaction. In choice (d), rate of reaction depends on 1st power of

C H_{3} C O O C H_{3}

and NaOH both.

Question 13. For reaction: A + B

\to

Products, the rate if the reaction at various concentration are given below:

\begin{matrix} E x p t . N o . & (A) & (B) & R a t e 1 & 0.2 & 0.2 & 2 2 & 0.2 & 0.4 & 4 3 & 0.6 & 0.4 & 36 \end{matrix}

Rate =k[A]2[B]2
Rate =k[A]2[B]
Rate =k[A][B]2
Rate =k[A]3[B]

Discuss Question

Answer: Option B. -> Rate =k[A]2[B]
:
B
Let the rate law be

r = k [A]^{x} [B]^{y}

Divide (2) by (1)

∴ 2 = [2] y, y = 1

Divide (3) by (2)

∴ 9 = (3)^{x}, x = 2

Hence rate equation,

R = k [A]^{2} [B]^{1}

Question 14. A chemical reaction was carried out at 300 K and 280 K. The rate constants were found to be

K_{1}

and

K_{2}

respectively then

K2≈0.5K1
K2≈0.25K1
K2≈2K1
K2≈4K1

Discuss Question

Answer: Option B. -> K2≈0.25K1
:
B
Let the rate constant at 300 K be

K_{1}

. Temperature decrease of

10^{\circ} C

, rate constant value becomes approximately half the original value.
Decrease in temperature =

20^{\circ} C

The rate constant,

K_{2}

at 280 C is

K_{2} = 0.25 K_{1}

K_{2} = 0.25 K_{1}

Question 15. The data for the reaction is A + B

\to

C is

\begin{matrix} E x p . & [A]_{0} & [B]_{0} & I n i t i a l r a t e 1 & 0.012 & 0.035 & 0.10 2 & 0.024 & 0.035 & 0.80 3 & 0.012 & 0.070 & 0.10 4 & 0.024 & 0.070 & 0.80 \end{matrix}

r=k[B]3
r=k[A]3
r=k[A][B]4
r=k[A]2[B]2

Discuss Question

Answer: Option B. -> r=k[A]3
:
B
A quick way to solve this would be to look at rows one and two. Straight away you can tell that rate does not depend on [B]

Question 16. For the reaction A + B

\to

C, it is found that doubling the concentration of A increases the rate by 4 times and doubling the concentration of B doubles the reaction rate. What is the overall order of the reaction?

Discuss Question

Answer: Option C. -> 3
:
C
rate =

k [A]^{x} [B]^{y}

\begin{matrix} 4 = k [2]^{x} & 2 = k [2]^{y} x = 2 & y = 1 \end{matrix}

Question 17. If in the fermentation of sugar in an enzymatic solution which is initially 0.12 M the concentration of sugar is reduced to 0.06 M in 10 h and to 0.03 M in 20 h, hence order of the reaction is

Discuss Question

Answer: Option B. -> 1
:
B

t_{1 / 2}

is constant. Hence order = 1

Question 18. Which of these does not influence the rate of reaction?

Nature of the reactants
Concentration of the reactants
Temperature
Order of a reaction

Discuss Question

Answer: Option D. -> Order of a reaction
:
D
Order of a reaction is equal to the sum of thestoichiometric coefficients expressed in a rate law.

Question 19. One litre of 2M acetic acid is mixed with one litre of 3M ethyl alcohol to form ester

C H_{3} C O O H + C_{2} H_{5} O H \Leftrightarrow C H_{3} C O O C_{2} H_{5} + H_{2} O

. The decrease in the initial rate if each solution is diluted by an equal volume of water would be

0.5 times
2 times
4 times
0.25 times

Discuss Question

Answer: Option C. -> 4 times
:
C
When each solution is diluted by equal volume of water, the concentration of each chemical is reduced to half the original.
We assume that this is an elementary reaction which leads to the conclusion that the order of this reaction would be 2.
The rate equation is