Question

the reaction of carbon monoxide and oxygen to give carbon dioxide 2CO(g)+O2(g)→2CO2(g)

has ΔrH°=-595.968 kJ mol-1 and ΔrS°=-172.938 J mol-1 K-1.

Is this process

Spontaneous at all temperatures

Spontaneous at low temperatures but not spontaneous at high temperatures

Not spontaneous at low temperatures but spontaneous at high temperatures

Not spontaneous at any temperature

Answer 1

Gibs free energy,

Δ_rG⁰ = Δ_rH⁰ - TΔ_rS⁰

Given that,

ΔrH°= - 595.968 kJ mol-1

and

ΔrS°= - 172.938 J mol-1 K-1.

For a spontaneous reaction Δ_rG⁰ = negative

SInce ΔrS° is given negative value, - TΔrS° will be a positive value.

Hence as long as Δ_rH⁰ > TΔrS° the reaction will be spontaneous. It is possible at low temperatures only. As the temperature increases TΔrS° value also increases which causes positive Δ_rG⁰ value making the reaction non spontaneous.

Hence,

Spontaneous at low temperatures but not spontaneous at high temperatures