Calculate Delta G 0 for The Reaction

What is ΔG°?

The standard Gibbs free energy change (ΔG°) is a fundamental thermodynamic property that measures the maximum amount of non-expansion work a system can perform under standard conditions. It's a key indicator of reaction spontaneity and energy transfer.

ΔG° is calculated under standard conditions (25°C, 1 atm pressure) and is expressed in kilojoules per mole (kJ/mol). A negative ΔG° indicates a spontaneous reaction, while a positive ΔG° suggests a non-spontaneous reaction.

How to Calculate ΔG°

To calculate ΔG° for a reaction, you need to know the standard Gibbs free energies of formation (ΔG°f) for all reactants and products. The calculation involves summing these values and applying the stoichiometric coefficients of the balanced chemical equation.

Steps to Calculate ΔG°

1. Write the balanced chemical equation for the reaction
2. Look up the standard Gibbs free energies of formation for all reactants and products
3. Multiply each ΔG°f by its stoichiometric coefficient
4. Sum the products for all reactants (ΔG°reactants) and all products (ΔG°products)
5. Calculate ΔG° using the formula: ΔG° = ΣΔG°products - ΣΔG°reactants

Formula

Where:

• ΔG° = standard Gibbs free energy change for the reaction (kJ/mol)
• ΔG°products = sum of standard Gibbs free energies of formation for all products
• ΔG°reactants = sum of standard Gibbs free energies of formation for all reactants

Example Calculation

Let's calculate ΔG° for the reaction: 2H₂(g) + O₂(g) → 2H₂O(g)

Standard Gibbs free energies of formation:

• H₂(g): 0 kJ/mol
• O₂(g): 0 kJ/mol
• H₂O(g): -237.1 kJ/mol

Calculation:

This negative value indicates the reaction is spontaneous under standard conditions.

Interpreting Results

The sign of ΔG° provides crucial information about reaction spontaneity:

• ΔG° < 0: The reaction is spontaneous and will occur without external energy input
• ΔG° = 0: The reaction is at equilibrium
• ΔG° > 0: The reaction is non-spontaneous and requires energy input to proceed

Understanding ΔG° helps chemists predict reaction feasibility, design efficient processes, and optimize energy use in chemical systems.