What is the Difference Between Gibbs Free Energy and Standard Free Energy?

The main difference between Gibbs free energy and standard free energy lies in the conditions under which they are calculated and applied. Here are the key differences:

1. Conditions: Gibbs free energy (ΔG) is a general expression that combines enthalpy and entropy into a single value, and it depends on the reactants' nature and concentrations. In contrast, standard free energy (ΔG°) is calculated under standard conditions, which are typically 1 bar and 298 K.
2. Non-zero value: ΔG is not a non-zero value, whereas ΔG° is a non-zero value.
3. Temperature and pressure dependence: Standard free energy changes (ΔG°) are dependent on temperature (T) and pressure, while non-standard free energy changes (ΔG) can be calculated using the equation ΔG = ΔG° + RT ln Q, where R is the gas constant, T is the temperature in Kelvin, and Q is the reaction quotient.
4. Application: The standard change in free energy (ΔG°) applies only when the reactants and products are in their standard states. In all other circumstances, the non-standard free energy change (ΔG) must be considered.

In summary, Gibbs free energy (ΔG) is a general expression that depends on the specific conditions and concentrations of reactants, while standard free energy (ΔG°) is a specific value calculated under standard conditions. The non-standard free energy change (ΔG) is used to determine the spontaneity of a reaction under non-standard conditions, taking into account temperature and pressure dependence.

Comparative Table: Gibbs Free Energy vs Standard Free Energy

Gibbs free energy and standard free energy are both thermodynamic quantities that describe the spontaneity of chemical reactions. Here is a table highlighting the differences between them:

In summary, Gibbs free energy depends on the experimental conditions, while standard free energy is calculated under standard conditions (1 atm pressure and 1 M concentrations). Both quantities can be used to determine the spontaneity of a reaction, with a positive value indicating a non-spontaneous reaction and a negative value indicating a spontaneous reaction.