Work done by the system in isothermal reversible process is `w_(rev.)= -2.303 nRT "log"(V_(2))/(V_(1))`. Also in case of adiabatic reversible process work done by the system is given by: `w_(rev.) = (nR)/(gamma -1) [T_2 - T_1]`. During expansion disorder increases and the increase in disorder is expressed in terms of change in entropy `DeltaS = q_(rev.)/T`. The entropy changes also occurs during transformation of one state to other end expressed as `DeltaS = DeltaH/T`. Both entropy and enthalpy changes obtained for a process were taken as a measure of spontaniety of process but finally it was recommended that decrease in free energy is responsible for spontaniety and `DeltaG=DeltaH - T DeltaS`. A chemical change will definitely be spontaneous if:A. `Delta H = -ve, Delta S = -ve` and low temperatureB. `Delta H = +ve, Delta S = -ve` and high temperatureC. `Delta H = -ve, Delta S = +ve` and any temperatureD. `Delta H = +ve, Delta S = +ve` and `T Delta S lt Delta H`