1

### JEE Main 2019 (Online) 9th January Morning Slot

The following results were obtained during kinetic studies of the reaction ;
2A + B $\to$ Products

Experiment [A] (in mol L$-$1) [b] (in mol L$-$1) Initial Rate of reaction
(In mol L$-$1 min$-$1)
I 0.10 0.20 6.93 G 10$-$3
II 0.10 0.25 6.93 G 10$-$3
III 0.20 0.30 1.386 G 10$-$2

The time (in minutes) required to consume half of A is :
A
5
B
10
C
1
D
100

## Explanation

Rate (r) = K[A]x [B]y

From experienced (I),

6.93 $\times$ 10$-$3 = K (0.1)x (0.2)y . . . . (1)

From experiment (II),

6.93 $\times$ 10$-$3 = K(0.1)x (0.25)y . . . . . (2)

equation (1) and (2) satisfies when y = 0

From experiment (III),

1.386 $\times$ 10$-$2 = K (0.2)x (0.30)y

$\Rightarrow$   1.386 $\times$ 10$-$2 = K(0.2)x . . . . . .(3)

Dividing (2) by (3) we get,

${1 \over 2} = {\left( {{1 \over 2}} \right)^x}$

$\Rightarrow$   x = 1

$\therefore$   Rate (r) = K (0.1)1 (0.2)0

$\Rightarrow$  6.93 $\times$ 10$-$3 = K (0.1)

$\Rightarrow$   K = 6.93 $\times$ 10$-$2

Now,

${t_{{1 \over 2}}} = {{0.693} \over {{K}}}$

= ${{0.693} \over {K}}$

= ${{0.693} \over {6.93 \times {{10}^{ - 2}}}}$

= 10

To consume half of A it becomes 10/2 = 5 min
2

### JEE Main 2019 (Online) 9th January Evening Slot

For the reaction, 2A + B $\to$ products, when the concentrations of A and B both were doubled, the rate of the reaction increased from 0.3 mol L$-$1s$-$1 to 2.4 mol L$-$1s$-$1. When the concentration of A alone is doubled, the rate increased from 0.3 mol L$-$1s$-$1 to 0.6 mol L$-$1s$-$1.
A
Total order of the reaction is 4
B
Order of the reaction with respect to B is 2
C
Order of the reaction with respect to B is 1
D
Order of the reaction with respect to A is 2

## Explanation

$r = K{\left[ A \right]^x}{\left[ B \right]^y}$

$\Rightarrow 8 = {2^3} = {2^{x + y}}$

$\Rightarrow x + y = 3\,...(1)$

$\Rightarrow 2 = {2^x}$

$\Rightarrow x = 1,y = 2$

Order w.r.t. A = 1

Order w.r.t. B = 2
3

### JEE Main 2019 (Online) 9th January Evening Slot

Consider the following reversible chemical reactions :

The relation between K1 and K2 is :
A
K1K2 = ${1 \over 3}$
B
K2 = K13
C
K2 = K1$-$3
D
K1K2 = 3

## Explanation

4

### JEE Main 2019 (Online) 10th January Morning Slot

Which of the graphs shown below does not represent the relationship between incident light and the electron ejected from metal surface ?
A
B
C
D

## Explanation

E = W + ${1 \over 2}$mv2

K.E. = hv $-$ 4v0

K.E. = hv + ($-$ hv0)

y = mx + $\underline C$