Question

Ethanol, C2H5OH, is promoted as a clean fuel and is used as an additive in many gasoline mixtures. Calculate the ΔH°rxn for the combustion of ethanol.

Substance ΔH°f(kJ/mol)
A. C2H5OH(l) –277.0
B. CO2(g) –393.5
C. H2O(g) –241.8

Answer 1

The ΔH°rxn for the combustion of ethanol is -1367.5 kJ/mol.

Step-by-step explanation:

The balanced equation for the combustion of ethanol is:

C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)

To calculate the ΔH°rxn for the combustion of ethanol, we need to use the enthalpies of formation of the reactants and products. The enthalpy of formation for ethanol, C₂H₅OH, is -277.0 kJ/mol. The enthalpy of formation for CO₂(g) is -393.5 kJ/mol, and the enthalpy of formation for H₂O(g) is -241.8 kJ/mol.

Using these values, we can calculate the ΔH°rxn using the equation:

ΔH°rxn = [2 × ΔH°f(CO₂)] + [3 × ΔH°f(H₂O)] - [ΔH°f(C₂H₅OH)]

ΔH°rxn = [2 × -393.5] + [3 × -241.8] - [-277.0] = -1367.5 kJ/mol

Therefore, the ΔH°rxn for the combustion of ethanol is -1367.5 kJ/mol.