Question

In the presence of a catalyst, the heat evolved or absorbed during the reaction_____________

• A. remains unchanged.
• B. increases
• C. decreases.
• D. may increase or decrease.

Answer 1

The correct option is A remains unchanged.

The substance which increases the rate of reaction without being consumed in the chemical reaction is called a catalyst.


A catalyst only lowers the required activation energy for the reactions. Since it lowers the activation energy for both the forward and reverse reactions to the same extent, the net change in enthalpy is zero.

$\Delta H=E_{a\left(forward\right)}-E_{a\left(Backward\right)}=0$

Hence, the enthalpy change value of the reaction will not be affected by a catalyst. So, option (C) is correct.