Calculate Standard Free Energy for The Following Reaction

What is Standard Free Energy?

Standard free energy (ΔG°) represents the maximum amount of useful work that can be obtained from a chemical reaction under standard conditions (25°C, 1 atm pressure, and 1 M concentration for all reactants and products). It's calculated using the standard Gibbs free energy values of formation (ΔG°f) for all reactants and products.

The sign of ΔG° indicates the spontaneity of the reaction:

• ΔG° < 0: Reaction is spontaneous and will proceed as written
• ΔG° = 0: Reaction is at equilibrium
• ΔG° > 0: Reaction is non-spontaneous as written

How to Calculate Standard Free Energy

To calculate ΔG° for a reaction, you need:

1. The balanced chemical equation
2. Standard Gibbs free energy of formation (ΔG°f) values for all reactants and products
3. The stoichiometric coefficients from the balanced equation

The calculation involves summing the ΔG°f values for all products and subtracting the sum of ΔG°f values for all reactants, each multiplied by their stoichiometric coefficients.

Formula

All ΔG°f values must be in the same units (typically kJ/mol or kcal/mol) and under the same standard conditions.

Example Calculation

Let's calculate ΔG° for the reaction:

2H₂ + O₂ → 2H₂O

Given standard Gibbs free energy of formation values:

• ΔG°f(H₂) = 0 kJ/mol
• ΔG°f(O₂) = 0 kJ/mol
• ΔG°f(H₂O) = -237.1 kJ/mol

Calculation:

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

Interpreting Results

When you calculate ΔG°:

• A negative value means the reaction will proceed spontaneously
• A positive value means the reaction will not proceed spontaneously
• A zero value means the reaction is at equilibrium

Remember that ΔG° only applies to standard conditions. In real-world scenarios, factors like temperature, pressure, and concentration can affect the spontaneity of reactions.