Thermodynamics Solved Problems

Calculate ΔG at 290 K for the following reaction:

2NO(g)+O2(g)+2NO2(g)

Solution:

Given:

ΔH = -120kJ and ΔS = -150JK^-1

To make the unit of ΔS the same as ΔH, we have to convert the unit of ΔS as follows:
ΔS=−150J/K(1kJ=1000J)⇒ΔS=−0.15kJ/K

We know that,G=U+PV–TS⇒ΔG=ΔH–TΔS

So,ΔG=−120kJ–(290K)(−0.150kJ/K)⇒ΔG=−120kJ+43kJ⇒ΔG=−77kJ

Therefore, ΔG is -77kJ.