Question

Given a free energy change, how would you determine whether a reaction is exothermic or endothermic/ far from or close to equilibrium?

Answer 1

Ans. The decision is based on two types of free energy change-

I. Standard free energy change, dG⁰ : The standard free energy is calculated under standard conditions, for example- at 37.0⁰C, 1.0 atm, 1M concentrations in cell ; or, at 0.0⁰C, 1.0 atm, etc. in chemistry.

II. Experimental free energy change, dG : The experimental free energy change is calculated at the given experimental conditions. For example, concertation of most of solutes never is 1.0 M in the body or cells. Say, if we calculate free energy change for a reaction at [X] = 0.01M, the condition is said to be experimental.

Similarly, experimental free energy change for the same reaction may change depending on the temperature, etc.

# Determination of fate of reaction:

A. If dG > dG⁰           , then the reaction is endothermic and non-spontaneous

B. If dG < dG⁰            , the reaction is exothermic and spontaneous

C. If dG = dG⁰           , the reaction is at equilibrium. No heat gained or lost.

# Greater is the difference between dG and dG⁰, farther is the reaction from equilibrium.

# Smaller is the difference between dG and dG⁰, closer is the reaction from equilibrium.