Use the chart below to answer the following question.

Substance
DGf º (kJ/mol)
C2H2 (g)
209.0
CO2 (g)
–394.0
H2O (l)
–237.0
O2 (g)
0.0


Which of the following represents the approximate change in standard free energy per mole for the combustion of C2H2 (g)?

–20 kJ/mol
+20 kJ/mol
–100 kJ/mol
–1200 kJ/mol
+1200 kJ/mol