Calculate Delta G 0

The standard Gibbs free energy change (ΔG°) is a fundamental concept in thermodynamics that measures the energy available to do work in a chemical reaction under standard conditions. This calculator helps you determine ΔG° using standard enthalpy and entropy values.

What is ΔG°?

ΔG° (Delta G naught) represents the change in Gibbs free energy for a chemical reaction under standard conditions (25°C and 1 atm pressure). It's calculated using the following formula:

ΔG° = ΔH° - TΔS°

Where:

ΔH° = Standard enthalpy change (kJ/mol)
T = Temperature in Kelvin (298.15 K at 25°C)
ΔS° = Standard entropy change (J/mol·K)

The Gibbs free energy change tells us whether a reaction is spontaneous (ΔG° < 0), non-spontaneous (ΔG° > 0), or at equilibrium (ΔG° = 0).

How to Calculate ΔG°

To calculate ΔG°:

Determine the standard enthalpy change (ΔH°) for the reaction
Determine the standard entropy change (ΔS°) for the reaction
Convert the temperature from Celsius to Kelvin (T = °C + 273.15)
Plug the values into the formula: ΔG° = ΔH° - TΔS°

Note: ΔH° and ΔS° values are typically found in chemistry textbooks or databases for standard reactions.

Interpreting ΔG° Results

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

ΔG° < 0: The reaction is spontaneous and will occur as written
ΔG° > 0: The reaction is non-spontaneous and will not occur as written
ΔG° = 0: The reaction is at equilibrium

The magnitude of ΔG° indicates the driving force of the reaction. Larger absolute values indicate stronger driving forces.

Example Calculation

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

Property	Value
ΔH°	-483.6 kJ/mol
ΔS°	-10 kJ/mol·K
Temperature (T)	298.15 K

Using the formula:

ΔG° = (-483.6 kJ/mol) - (298.15 K)(-10 kJ/mol·K)

ΔG° = -483.6 kJ/mol + 2981.5 kJ/mol

ΔG° = 2497.9 kJ/mol

Since ΔG° is positive, this reaction is non-spontaneous under standard conditions.

FAQ

What units should I use for ΔH° and ΔS°?

ΔH° should be in kilojoules per mole (kJ/mol) and ΔS° should be in joules per mole per Kelvin (J/mol·K). The calculator will automatically convert these units to calculate ΔG° in kJ/mol.

Can I use this calculator for non-standard conditions?

No, this calculator is specifically for standard conditions (25°C and 1 atm pressure). For non-standard conditions, you would need to use the full Gibbs free energy equation that includes pressure and concentration terms.

What if I don't know ΔH° and ΔS° for my reaction?

You can calculate ΔH° and ΔS° from standard enthalpies and entropies of formation for the reactants and products. These values are typically found in chemistry textbooks or databases.