Question

Consider the reaction 2SO2(g) + O2(g) Right arrow. 2SO3(g).

Substance
Delta.Hf (kJ/mol)
S (J/(molmc021-3.jpgK))
SO3(g)
–396
130.58
SO2(g)
–297
191.50
O2(g)
0
205.00

What is the Delta.Grxn of this reaction, and would it be spontaneous or nonspontaneous at 300.0 K? Use Delta.G = Delta.H – TDelta.S.
–296 kJ/mol, spontaneous
–296 kJ/mol, nonspontaneous
–100 kJ/mol, spontaneous
–100 kJ/mol, nonspontaneous

Answer 1

Calculate enthalpy and entropy changes, then ΔG = ΔH − TΔS.

ΔH = 2(−396) − [2(−297) + 0] = −792 − (−594) = −198 kJ

ΔS = 2(130.58) − [2(191.50) + 205.00] = 261.16 − 588.00 = −326.84 J/K = −0.32684 kJ/K

TΔS (300.0 K) = 300.0(−0.32684) = −98.05 kJ

ΔG = −198 − (−98.05) = −99.95 kJ ≈ −100 kJ

Since ΔG < 0, the reaction is spontaneous at 300.0 K.

Answer: −100 kJ/mol, spontaneous.