Question

24 and 25

24) Endothermic reaction; increase in entropy
Calculate the equilibrium constant at 31 K for a reaction with ΔHrxno = 10 kJ and ΔSrxno= 100 J/K.

25)

Calculate the equilibrium constant at 129 K for the thermodynamic data in the previous question.

Notice that Keq is dramatically larger for a larger temperature when there is a substantial positive increase in entropy.

Answer 1

24)

deltaH = 10.0KJ/mol

deltaS = 100J/mol.K

= 0.1 KJ/mol.K

T = 31 K

we have below equation to be used:

deltaG = deltaH - T*deltaS

deltaG = 10.0 - 31.0 * 0.1

deltaG = 6.9 KJ/mol

=6900 J/mol

T = 31 K

we have below equation to be used:

deltaG = -R*T*ln Kc

6900 = - 8.314*31.0* ln(Kc)

ln Kc = -26.7718

Kc = 2.36*10^-12

Answer: 2.36*10^-12

25)

deltaH = 10.0KJ/mol

deltaS = 100J/mol.K

= 0.1 KJ/mol.K

T = 129 K

we have below equation to be used:

deltaG = deltaH - T*deltaS

deltaG = 10.0 - 129.0 * 0.1

deltaG = -2.9 KJ/mol

= -2900 J/mol

T = 129 K

we have below equation to be used:

deltaG = -R*T*ln Kc

-2900 = - 8.314*129.0* ln(Kc)

ln Kc = 2.7039

Kc = 14.9

Answer: 14.9