Entropy: A Level Chemistry Definition

What is entropy?

Entropy (S) is a measure of the disorder or randomness of a system. The greater the disorder, the higher the entropy.

In A Level Chemistry, entropy is crucial for understanding spontaneity in chemical reactions. Gases have higher entropy than liquids and solids due to the greater freedom of particle movement. Entropy change (ΔS) is positive when a system becomes more disordered, such as when a solid dissolves or a reaction produces more gas molecules.

Entropy change can be calculated using:

ΔS_system^ꝋ = ΣΔS_products^ꝋ - ΣΔS_reactants^ꝋ

(where Σ = sum of)

The feasibility of a reaction depends on both entropy and enthalpy, as shown in the Gibbs free energy equation (ΔG = ΔH - TΔS). Understanding entropy helps explain why some reactions occur spontaneously, even if they are endothermic.

Entropy Revision Resources to Ace Your Exams

For more information about entropy check out the following resources:

• Entropy- A level Revision Notes

• Thermodynamics- A Level Multiple Choice Questions

• Thermodynamics- A Level Exam Questions

Explore our A level Chemistry Revision Resources