Question

Determine whether the reaction with the following ∆H and ∆S value are spontaneous or Non spontaneous.State wheather they are exothermic or endothermic. a)∆H=-110kj and ∆S=+40kj at 400k.b)∆H=+50kj and ∆S=-130kj at 250k.​

Answer 1

(a) Given: ΔH=−110kJ

ΔS=40Jk−1

=0.04KJk−1

Temperature, T=4000K

ΔG=?

Since ΔH is −Ve, the reaction is exothermic

ΔG=ΔH−TΔS

=−110−400×0.04

=−110−16

=−126kJ

Since, ΔG is negative, the reaction is spontaneous and exothermic.

(b) Given: ΔH=40kJ,

ΔS=−120Jk−1=−0.12KJk−1

Temperature, T=250K

ΔG=?

Since ΔH is +ve, the reaction is endothermic.

ΔG=ΔH−T.ΔS

=40−250×(−0.12)

=40+30

=70kJ.

Since ΔG>0, the reaction is non-spontaneous

ΔG=70kJ; The reaction is endothermic and non-spontaneous.