Entropy increase in a process
a) In a chemical reaction, when number of molecules of products are more than the number of molecules of reactant entropy increases.
b) In physical process, when a solid changes to liquid, when a liquid changes to vapour and when a solid changes to vapour, entropy increase in all these processes.
Example
1 mole of an ideal gas maintained at 4.1 atm and at a certain temperature absorbs 3710J heat and expands to 2 litres. Calculate the entropy change in expansion process.
For 1 mole of an ideal gas,
PV = RT, P = 4.1 atm V = 2 lit
Temperatur e = [4.1atm 2lit 1mole] / [0.082 lit atm K-1 mol-1]
= 100 K.
ΔS = q/T = [3710 J / 100 K] = 37.1 J K-1 mol-1
ΔS of expansion = 37.1 J K-1 mol-1.
