1

### 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 + $\underline C$
2

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

Consider the given plots for a reaction obeying Arrhenius equation (0oC < T < 300oC) : (K and Ea are rate constant and activation energy, respectively) Choose the correct option :
A
I is right but II is wrong
B
Both I and II are correct
C
Both I and II are wrong
D
I is wrong but II is right

## Explanation

Arrhenius Equation -

Arrhenius gave the quantitative dependence of rate constant on temperature by the Arrhenius equation.

- wherein

$k = A{e^{ - {E_a}/RT}}$

${\mathop{\rm lnk}\nolimits} = lnA - {{{E_a}} \over {RT}}$

k = Rate constant

as we have learned in Arrhenius equation when we increase Ea, K should decrease As T increases, power of exponential increases so k also increase.

Hence, both the plots are correct.
3

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

For an elementary chemical reaction, the expression for ${{d\left[ A \right]} \over {dt}}$ is
A
2K1[A2] – K –1 [A]2
B
K1[A2] – K –1 [A]2
C
K1[A2] + K –1 [A]2
D
2K1[A2] – 2K –1 [A]2

## Explanation 4

### JEE Main 2019 (Online) 11th January Morning Slot

If a reaction follows the Arrhenius equation, the plot ln k vs ${1 \over {\left( {RT} \right)}}$ gives straight line with a gradient ($-$ y) unit.

The energy required to active the reactant is :
A
y unit
B
y/R unit
C
yR unit
D
$-$y unit

## Explanation

According to Arrhenius equation,
k = A${e^{ - {{{E_a}} \over {RT}}}}$

or ln k = ln A - ${{{{E_a}} \over {RT}}}$

Comparing the above equation with straight line equation,

y = mx + c,

we get, slope or gradient (m) = –Ea
and Intercept (c) = ln A

Also given that slope or gradient (m) = -y

$\therefore$ -y = –Ea

$\Rightarrow$ Ea = y

So the activation energy of the reactant, Ea = y unit