Question

1. The equilibrium point of any chemical reaction represents the most energetically stable state in the continuum of conditions between pure reactants and pure products. Explain, using the concept of enthalpy (energy) of reaction, why this is the case.

Answer 1

Enthalpy change of a reaction (H) : It is flow of heat into the system from the surroundings at constant pressure.

A chemical reaction which include enthalpy change is known as thermochemical reaction. It might be either positive or negative.

A chemical reaction that has positive sign value is known as endothermic reaction wheras negative sign value is known as exothermic reaction.

For endothermic reactions, where in the system chemical reaction occurs by gaining energy/absorbing energy. Here energy of the reactants slowly increases its energy as it goes to produce products.

For exothermic reactions, where in the system chemical reaction occurs by losing energy. Here energy of the reactants slowly increases its energy as it goes to produce products.

The enthalpy or potential energy of a substance or compound is compared relatively with that of reference state. Transition state is the energy barrier between the reactants and products which is unstableso reaction continues to convert the reactants to products. Wheras at equilibrium the reactant is not able to work because the concentration of reactants and products are in equilibrium and there is no change in properties of the system where gibbs free energy is zero.

All chemical systems tend to minimise the gibbs free energy and makes the system stable. But at equilibrium as the gibbs free energy is 0, the system makes stable and no further reactions either forward or backward reaction does not ocuurs.

then G = H-TS

0 = H-TS ===> H = TS at equilibrium