Question

The sign of ΔHrxn and ΔSrxn for several different reactions are given.

In which case is the reaction spontaneous at all temperatures?

ΔHrxn<0; ΔSrxn>0ΔHrxn<0; ΔSrxn<0ΔHrxn>0; ΔSrxn<0ΔHrxn>0; ΔSrxn>0

Answer 1

Answer – We know the change in the enthalpy is negative and change in entropy is positive of the reaction then the reaction is spontaneous at all temperatures, since we know the formula

∆G^o = ∆H^o -T∆S^o

So when ∆H^o_rxn < 0 and ∆S^o_rxn > 0 means ∆H^o_rxn negative and ∆S^o_rxn is positive, then there is ∆H^o -T∆S^o come negative so, ∆G^o is negative and reaction is spontaneous at all temp.

So, ΔHrxn<0; ΔSrxn>0 is the case where reaction spontaneous at all temperatures.