# Thermodynamic - Gibbs Free Energy (A-Level Chemistry)

# Gibbs Free Energy

## Gibbs Free Energy

### Key Terms

**Enthalpy** – Heat exchanged between the system and the surroundings at a constant pressure during a chemical reaction

**Entropy** – Measure of disorder or randomness of a system

**Gibbs Free Energy** – Energy change that takes into account both the entropy change and the enthalpy change.

### Gibbs Free Energy Change, ΔG

As we learnt in previous chapters, a reaction’s **feasibility** depends on two factors: the **enthalpy change**, ΔH, and the **entropy change**, ΔS.

We can use these factors in an equation to determine whether a reaction will occur **spontaneously**. This equation calculates the **Gibbs Free Energy change**.

Where:

ΔG = change in Gibbs free energy, kJ mol-1

ΔH = change in enthalpy, kJ mol-1

ΔSsystem = change in entropy, J K-1 mol-1

T = Temperature, Kelvin

### Reaction Feasibility and ΔG

If the value of ΔG is **positive**, the reaction is **not feasible**.

If the value of ΔG is **zero** or **negative**, the reaction is **feasible**.

There are however some limitations to this predictions as ΔG does not take **reaction rate** into account: if a reaction has a very **high activation energy**, reaction rate would be so slow that you would not notice the reaction was taking place, even if ΔG was negative.

**→What is Gibbs Free Energy in A-Level Chemistry?**

Gibbs Free Energy is a measure of the amount of energy available to do useful work in a chemical reaction. It is an important topic in A-Level Chemistry as it helps to understand the direction and feasibility of chemical reactions.

**→How is Gibbs Free Energy related to chemical reactions?**

Gibbs Free Energy is related to chemical reactions because it determines whether a reaction is spontaneous (i.e., will occur without the input of additional energy) or non-spontaneous (i.e., will not occur without the input of additional energy).

**→What is the equation for Gibbs Free Energy?**

The equation for Gibbs Free Energy is: ΔG = ΔH – TΔS, where ΔG is the change in Gibbs Free Energy, ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.

**→How is Gibbs Free Energy related to enthalpy and entropy?**

Gibbs Free Energy is related to enthalpy and entropy because it takes into account both the heat released or absorbed during a chemical reaction (enthalpy) and the disorder or randomness of the system (entropy).

**→What does a negative value of ΔG mean?**

A negative value of ΔG means that the reaction is spontaneous and will occur without the input of additional energy.

**→What does a positive value of ΔG mean?**

A positive value of ΔG means that the reaction is non-spontaneous and will not occur without the input of additional energy.

**→What is the significance of the magnitude of ΔG?**

The magnitude of ΔG determines the rate and extent of the reaction. The larger the magnitude of ΔG, the slower and less complete the reaction will be.

**→How can Gibbs Free Energy be used to predict the feasibility of a reaction?**

Gibbs Free Energy can be used to predict the feasibility of a reaction by comparing the ΔG of the reactants to the ΔG of the products. If the ΔG of the products is lower than the ΔG of the reactants, the reaction will be spontaneous and feasible.

**→What is the relationship between Gibbs Free Energy and equilibrium?**

Gibbs Free Energy is related to equilibrium because at equilibrium, the Gibbs Free Energy of the system is at a minimum. Therefore, the value of ΔG can be used to determine the position of equilibrium and the direction in which the reaction will proceed to reach equilibrium.

**→What is the importance of Gibbs Free Energy in industrial processes?**

Gibbs Free Energy is important in industrial processes because it allows for the optimization of reaction conditions to maximize the yield of desired products while minimizing energy input and waste.

## Still got a question? Leave a comment

## Leave a comment