Ethanol can be prepared in several ways. It can be produced during alcohol fermentation (Reaction A). It is also produced commercially from ethylene (Reaction B). Calculate the ΔG°_rxn (kJ•mol^–1) of each reaction.
A. C₆H₁₂O₆(s) → 2 C₂H₅OH(l) + 2 CO₂(g)
B. C₂H₄(g) + H₂O(g) → C₂H₅OH(l)
Determine which method requires less energy under standard conditions.
Substance            ΔG°_f (kJ/mol)
C₆H₁₂O₆(s)           –910.4
C₂H₄(g)                   68.4
C₂H₅OH(l)           –174.8
H₂O(g)                 –228.6
CO₂(g)                 –394.4

• A. A) –228 kJ/mol; B) –14.6 kJ/mol; Reaction B requires less energy under standard conditions.
• B. A) –228 kJ/mol; B) –14.6 kJ/mol; Reaction A requires less energy under standard conditions.
• C. A) –166.4 kJ/mol; B) 471.8 kJ/mol; Reaction B requires less energy under standard conditions.
• D. A) –166.4 kJ/mol; B) 471.8 kJ/mol; Reaction A requires less energy under standard conditions.

Answer: (B)