2001 AIPMT Chemical KineticsCatalysis and Activation Energy Medium Question 78 of 80 in Chemical Kinetics

When a biochemical reaction is carried out in laboratory outside the human body in the absence of enzyme, then the rate of reaction obtained is $10^{-6}$ times, then activation energy of reaction in the presence of enzyme is : -

A $\dfrac{6}{RT}$
B P is required
C Different from $E_a$ obtained in laboratory
D Can't say anything

The answer is C.

Solution

An enzyme is a biological catalyst. It provides an alternative reaction path with a lower activation energy.
Without the enzyme (in the laboratory), the rate is only $10^{-6}$ times the rate with the enzyme, which shows that the activation energy without the enzyme is much higher.
From the Arrhenius equation, $\dfrac{k_{enzyme}}{k_{lab}} = e^{(E_{a,lab} - E_{a,enzyme})/RT} = 10^6$, so $E_{a,lab} - E_{a,enzyme} = 2.303 \times 6RT$.
So the activation energy in the presence of the enzyme is different from (lower than) the $E_a$ obtained in the laboratory.

Concept Enzymes lower activation energy

Chemical Kinetics in past papers

80 questions from this chapter have appeared across 26 exam years.