Question

How does total entropy change for a spontaneous process? 

How does Free Energy change in a spontaneous process? 

How is Free Energy Related to Equilibrium?

Answer 1

1. Total entropy change for a spontaneous process

Entropy of a system is a measure of degree of randomness/disorder of the system. A spontaneous process is the process which occurs on its own without any external driving force.

According to second law of thermodynamics, the total entropy change of universe for a spontaneous process is always positive. Mathematically,

Or

Where =Total entropy change of universe (sum of entropy change of system and surroundings)

=Entropy change of the system under consideration

=Entropy change of the surroundings of the system under consideration

2) Free energy change in a spontaneous process

Free energy is the energy of a reaction which is available to do work. It is defined as enthalpy of reaction -product of temperature and the entropy of the reaction. Free energy change is therefore the enthalpy change of the reaction - product of temperature and entropy change of the system

Free energy change for a spontaneous process is always negative. Mathematically,

Where =Free energy change for the process

Or

Where =Enthalpy change of reaction

T=temperature of the reaction

=Entropy change of reaction

3) Relation of free energy change to equilibrium

Equilibrium is that state when the rate of forward reaction becomes equal to rate of backward reaction i.e. when the rate of formation of products=rate of formation of reactants. At this stage, the concentrations of reactants and products appear to be constant. At equilibrium free energy change is equal to 0. Also the relationship of free energy change with equilibrium constant is given as

Where =Standard free energy change at equilibrium

R=Gas constant=8.314 J/molK

T=Temperature in K

K_eq=Equilibrium constant