Calculate Δg Δg at 298 K for The Following Reactions

The Gibbs free energy change (ΔG) at 298 K is a fundamental thermodynamic property used to determine the spontaneity of chemical reactions. This calculator helps you compute ΔG for any reaction using standard Gibbs free energy values of the reactants and products.

How to calculate ΔG at 298 K

To calculate the Gibbs free energy change for a reaction at 298 K (25°C), you need to know the standard Gibbs free energy values (ΔG°) of the reactants and products. The calculation involves summing the ΔG° values of the products and subtracting the sum of the ΔG° values of the reactants.

Note: All values should be in the same units (typically kJ/mol) and at the same temperature (298 K).

Steps to calculate ΔG

Identify the balanced chemical equation for the reaction.
Look up the standard Gibbs free energy values (ΔG°) for each reactant and product.
Multiply each ΔG° value by the stoichiometric coefficient from the balanced equation.
Sum the ΔG° values for the products (ΔG°products).
Sum the ΔG° values for the reactants (ΔG°reactants).
Calculate ΔG for the reaction using the formula: ΔG = ΔG°products - ΔG°reactants.

Formula

The standard Gibbs free energy change for a reaction is calculated using the following formula:

ΔG = Σ(ΔG°products) - Σ(ΔG°reactants)

Where:

ΔG is the Gibbs free energy change for the reaction
ΔG°products is the sum of the standard Gibbs free energy values of the products
ΔG°reactants is the sum of the standard Gibbs free energy values of the reactants

Example calculation

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

Compound	ΔG° (kJ/mol)	Stoichiometric Coefficient	ΔG° × Coefficient
H₂(g)	0	-2	0
O₂(g)	0	-1	0
H₂O(l)	-237.1	2	-474.2

Calculation:

ΔG = (2 × -237.1) - (2 × 0 + 1 × 0) = -474.2 kJ

The reaction is highly exergonic (ΔG = -474.2 kJ), meaning it is spontaneous and releases energy.

Interpreting the results

The sign of ΔG indicates the spontaneity of the reaction:

ΔG < 0: The reaction is spontaneous and exergonic (releases energy).
ΔG = 0: The reaction is at equilibrium.
ΔG > 0: The reaction is non-spontaneous and endergonic (requires energy input).

The magnitude of ΔG indicates the driving force of the reaction. Larger absolute values of ΔG indicate stronger spontaneity or the need for more energy input.

FAQ

What is the standard Gibbs free energy?

The standard Gibbs free energy (ΔG°) is the change in free energy that occurs when one mole of a substance is converted from its standard state to products under standard conditions (298 K, 1 atm pressure).

Where can I find standard Gibbs free energy values?

Standard Gibbs free energy values can be found in chemistry reference books, online databases like the NIST Chemistry WebBook, or thermodynamic tables.

What units are used for ΔG?

ΔG is typically measured in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).

Can ΔG be negative?

Yes, a negative ΔG indicates an exergonic reaction that releases energy.

How does temperature affect ΔG?

ΔG is temperature-dependent. The formula ΔG = ΔH - TΔS (where ΔH is enthalpy change and ΔS is entropy change) shows that ΔG changes with temperature.