Question

1. According to the Appendix at the back of the text:

ΔH∘f(kJ/mol) S∘(J/mol•K)

C3H8(g) –103.8 269.9

CO2(g) –393.5 213.8

H2O(l) –285.8 69.9

O2(g) 0.0 205.0

Using the standard heats of formation and the absolute entropies, calculate ΔG∘ (in units of kJ) for the following reaction at 300 K. answer in KJ.

C3H8(g) + 5O2(g)=3CO2(g)+4H2O(l)

Answer 1

H_r = 3*(-393.5)+4*(-285.8)-1*(-103.8) = -2221 kJ

S_r = 3*213.8+4*69.9-1*269.9-5*205 = -373 kJ

G = H - T*S = - 2221 - 300*(-0.373) = - 2109.1 kJ