**Units of entropy:** The dimension of entropy are energy in terms of heat X temperature-1. The entropy is expressed as calories per degree which is referred to as the entropy units (eu). Since entropy also depends on the quantity of the substance, unit of entropy is calories per degree per mole (or) eu. per mole.

cgs units of entropy is cal.K-1 denoted as eu. The SI unit is JK^{-1} and denoted EU. 1 eu = 4.184 EU.

viii) Entropy change is related to enthalpy change as follows:

For a reversible and isothermal process,

∆S_{rev} = ∆q_{rev}/T

Since ΔH is the heat absorbed (or) evolved in the process at constant T and pressure P.ΔS is also calculated from ΔH as ΔS = ΔH/T

where T is the temperature of the process involving ΔH, amount of enthalpy change, at constant pressure.