Class 11 NEET Chemistry Chemical Thermodynamics

Gas phase reaction
PCl5(g)⇌PCl3(g)+Cl2(g)
∆H=∆E+∆ngRT
∆ng= Change in number of moles of product and reactant species.
Since ∆ng=+ve, hence ∆H=+ve
also one mole of PCl5 is dissociated into two moles of PCl3 and Cl2 in the same phase.
Therefore, ∆S=S‌product ‌−S‌reactant ‌
∆S=+ ve.