1
COMEDK 2025 Afternoon Shift
MCQ (Single Correct Answer)
+1
-0
The time needed for completion of $80 \%$ is $y$ times the half-life period of a first order reaction. What is the value of $y$ ?
A
0.648
B
3.46
C
2.32
D
0.322
2
COMEDK 2025 Afternoon Shift
MCQ (Single Correct Answer)
+1
-0
Which one of the following is incorrect?
A
Rate constant equals the rate of reaction when concentration of reactants equals unity.
B
Larger the value of rate constant $(\mathrm{k})$ value faster is the chemical reaction.
C
The unit for rate constant for $n^{\text {th }}$ order reaction is $\left(\mathrm{mol} \mathrm{L}^{-1}\right)^{n-1} \mathrm{~s}^{-1}$
D
The value of rate constant $(\mathrm{k})$ is independent of concentration of reactants.
3
COMEDK 2025 Afternoon Shift
MCQ (Single Correct Answer)
+1
-0

(i) and (ii) are 2 chemical reactions carried out at TK.

(i). $\mathrm{X} \rightarrow \mathrm{Y}+\mathrm{W}$ with $\mathrm{k}_1$ as rate constant.

(ii). $\mathrm{X} \rightarrow \mathrm{Z}+\mathrm{W}$ with $k_2$ as rate constant.

The Activation energy for reaction (ii) is 3 times that of reaction (i). What is the expression for $k_1$ ?

A
$k_1=-2 k_2 e^{2 E a_1 / R T}$
B
$k_1=k_2 e^{2 E a_1 / R T}$
C
$k_1=2 k_2 e^{E a_1 / R T}$
D
$k_1=k_2 / 2 e^{-E a_1 / R T}$
4
COMEDK 2025 Afternoon Shift
MCQ (Single Correct Answer)
+1
-0
The rate constant for a zero order reaction $\mathrm{A} \rightarrow \mathrm{B}+\mathrm{C}$ is $6.0 \times 10^{-3} \mathrm{molL}^{-1} \mathrm{~s}^{-1}$. What would be the time taken for the initial concentration of A to decrease from 0.2 M to 0.024 M ?
A
15.83 s
B
37.34 s
C
31.90 s
D
29.33 s
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