The entropy of the system decreases on condensation of a vapour though it occurs spontaneously. Explain.

Explanation

On condenstaion of vapour, the entropy change of the system is, `DeltaS=S_("liquid")-S_("vapour")`. As `S_("liquid") lt S_("vapour")`, the entropy of the system decreases in the process. Condensation of a vapour is an exothermic process. Hence, the entropy of the surroundings increases. however the increase in entropy of the surroundings increases. however the increase in entropy of the surroundings is greater than the decrease in entropy of the system. So, `DeltaH_("total")` is always positive in this process.
`DeltaS_("total")=-DeltaS_("system")+DeltaS_("surroundings")`
So, condensation of a vapour is a spontaneous process.