Question

When ethanol (CH₃CH₂OH(l)) is combusted, such as when in a gasoline blend, the following reaction occurs:

2CH₃CH₂OH(l)+6O₂(g)-->4CO₂(g)+6H₂O(g)
Based on the standard Gibbs energies of formation, what is the standard Gibbs energy change for this reaction?
Substance ΔGf0 (kJ mol-1)
CH₃CH₂OH(l): -174.9
O₂(g): 0
CO₂(g): -394.4
H₂O(g): -228.6

Answer 1

The standard Gibbs energy change for the combustion of ethanol is -1599.4 kJ/mol.

Step-by-step explanation:

The standard Gibbs energy change (ΔG°) for a reaction can be calculated using the standard Gibbs energies of formation. In the reaction given, 2CH₃CH₂OH(l) + 6O₂(g) → 4CO₂(g) + 6H₂O(g), the change in standard Gibbs energy is equal to the sum of the standard Gibbs energies of formation of the products minus the sum of the standard Gibbs energies of formation of the reactants.

Using the given values:

ΔG° = (4 x ΔGf°(CO₂)) + (6 x ΔGf°(H₂O)) - (2 x ΔGf°(CH₃CH₂OH))

= (4 x -394.4 kJ/mol) + (6 x -228.6 kJ/mol) - (2 x -174.9 kJ/mol)

= -1577.6 kJ/mol + (-1371.6 kJ/mol) + 349.8 kJ/mol

= -1599.4 kJ/mol

So, the standard Gibbs energy change for the reaction is -1599.4 kJ/mol.