Calculate ΔG° for the combustion of propane. C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

Question

Quizplus · Accepted Answer

To calculate ΔG° for the combustion of propane using standard free energies of formation, we need to use the following equation:

ΔG° = ΣnΔG°f(products) - ΣnΔG°f(reactants)

Where:
- ΣnΔG°f(products) is the sum of the standard free energies of formation of the products, each multiplied by its stoichiometric coefficient.
- ΣnΔG°f(reactants) is the sum of the standard free energies of formation of the reactants, each multiplied by its stoichiometric coefficient.

Using the values for standard free energies of formation from a table of thermodynamic data, we get:

ΔG° = [3(-393.5 kJ/mol CO) + 4(0 kJ/mol H2O) + 5(0 kJ/mol O2) ] - [1(-393.5 kJ/mol CO2) + 3(-285.8 kJ/mol C3H8) + 5(0 kJ/mol O2) ]

ΔG° = [-1180.5 kJ/mol] - [-857.4 kJ/mol] = -323.1 kJ/mol

This is the ΔG° per mole of propane burned. To get the ΔG° for the combustion of one mole of propane, we need to multiply by the number of moles of propane involved in the reaction, which is 1. We then convert the result to kJ (by dividing by 1000 J/kJ) and round to one decimal place to get:

ΔG° = -323.1 kJ/mol × 1 mol/propane × (1 kJ/1000 J) ≈ -0.3 kJ/propane ≈ -0.6 kJ

Therefore, the best choice is A, as it is the closest approximation to the calculated value.

Calculate ΔG° for the Combustion of Propane