Question

How can I calculate delta G of a reaction?

Answer 1

Delta G is also known as change in Gibbs free energy which is the amount of useful energy required for the completion of chemical reaction. It is calculated by the help of enthalpy and entropy.

Complete Solution :
Suppose that for the completion of any chemical reaction in the system, we provide external energy in the form of heat by increasing or changing temperature of the system; due to which enthalpy as well as entropy of the chemical reaction also changes.
-Change in enthalpy means difference in the enthalpy of the reactant and the product of the chemical reaction.
-And change in entropy means there we observe randomness or irregular arrangement of the atoms involved in the chemical reaction.
-Gibbs free energy in particular temperature and at definite time is defined as the subtraction of the product of temperature and entropy from the enthalpy of the reaction.
${\text{G = H - TS}}$
Delta G or change in Gibbs free energy is calculated as:
$\Delta {\text{G = }}\Delta {\text{(H - TS)}}$
Or $\Delta {\text{G = }}\Delta {\text{H - T}}\Delta {\text{S}}$
-S.I. unit of Gibbs free energy is Kilojoule per mole or ${\text{KJmo}}{{\text{l}}^{{\text{ - 1}}}}$ , because it is a type of energy or calorie.

Additional information -
Gibbs free energy depends on the temperature, pressure as well as in volume also, because these three quantities connected to each other by the following relation:
${\text{PV = nRT}}$

Note: Here during the calculation of delta G of any reaction some of you may write delta in front of temperature also in the formula which will be wrong, because we are calculating delta G at particular time and at constant temperature.