Question

In Transition-state Theory of reaction rates, we can discuss the reaction between reactants and activated complex.
But I am stuck by the role of catalyst and its effect in transition state when we compare the rxn rate constant with Arrhenius equation.
(here a figure, the equation.)

Answer 1

At the last equation, it says the change in H is activated energy in Arrhenius equation.
I know catalysis can reduce activated energy of a reaction and entropy of the system, but I think the change in enthalpy of a reaction shouldn't change!?

Answer 2

if the enthalpy of a reaction changes then its entropy is already affected and vice versa.. consider gibbs equation. where enthalpy and entropy are inter related to each other.

Answer 3

Ya, but isn't the enthalpy between reactants and products constant of a reaction?

Answer 4

Q: How can a catalysis affect DS and DH of a reaction?

Answer 5

the enthalpy is constant but at constant temperature. when reaction is carried out with the change in enthalpy heat of reaction changes to vary the entropy and keep temperature constant.the change in transition state which is accompanied by change in temperature is multiplied by the entropy to make free energy feasible for the reaction to be carried out.

Answer 6

catalysis makes the entropy to stay at minimum. and thereby the reaction can take place at low temp and low enthalpy also.

Answer 7

Delta H reamains same irrespective of catalyst.

Answer 8

yes, i did thought Delta H is constant, but the figure i attached says it change!?

Answer 9

First let us analyze graph of a genral reaction without catalyst.
Now with catalyst Now notice That even though there is a dip in the curve in between the reaction will always reach a fixed final state. Delta H is a state function(Not a path function) Hence it stays same if end points are same.