You are experimenting on the effect of temperature on the rate of reaction between hydrochloric acid (HCl) and potassium iodide (KI). When the reaction is completed at 400K there are approximately 250,000 collisions per mole of reactant. You run the experiment again at 150K. Which of the following would you expect to be the number of collisions recorded at 150K

A. 0

B. 400,000

C. 250,000

D. 15,000

D. 15,000.

Explanation:

Kinetic energy of the molecules (of the reactants) is directly proportional to its temperature according to the relation:

KE = (3/2) KT

Where, KE is the kinetic energy of the molecules (J),

K is the Boltzmann constant (1.381 * 10⁻²³ J/K),

T is the temperature (K)

The KE (energy of motion of the molecules) can be expressed as the collisions per mole of reactant. When temperature increases, the collisions per mole of reactant and then the kinetic energy increases.

In this problem, at 400 K there are approximately 250,000 collisions per mole of reactant. So, at 150 K, the KE will decrease and also the collisions per mole of reactant will decrease. It is also impossible, for the collisions per mole of reactant, to be zero at this T (150 K).

So, the right choice is: D. 15,000