Question

The first order reaction of methyl isonitrile to form acetonitrile has a rate constant of k = 1.7 × 10−15 at 298 K. What will happen to the rate constant if the temperature is decreased to 100 K?

Answer 1

Answer : If the temperature is decreased to 100 K then the rate constant will be, decrease.

Explanation :

According to the Arrhenius equation,  the rate constant of the reaction is directly proportional to the temperature.

$K=a\times e^{\frac{-Ea}{RT}}$

Taking ln on both the sides, we get

$\ln K=\frac{-Ea}{RT}+\ln a$

where,

K = rate constant

Ea = activation energy

T = temperature

R = gas constant

a = Arrhenius constant

As we know that the increase in the rate of reaction with increase in the temperature is mainly due to increase in the number of effective collision. That means as the temperature increases, the number of effective collision increases and the value of rate constant also increases or vice-versa.

As per question, the temperature of the reaction decreases that means the number of effective collision decreases and the value of rate constant also decreases.

Hence, if the temperature is decreases from 298 K to 100 K then the rate constant will be, decrease.

Answer 2

Refer to to this chart 

Credits to https://image.slidesharecdn.com/nybf09-unit2slides26-57-100125181507-phpapp01/95/nyb-f09-unit-2-slid...

As temperature decreases, rate decreases. 

As temp increases, k also increases.