5.2.2 Enthalpy and Entropy: Module 5: Physical Chemistry & Transition Elements: Chemistry OCR A A Level

Define entropy.

A measure of the dispersal of energy in a system which is greater when the system is more disordered.

What is the symbol of entropy?

S

Solid or gas, which is more disordered?

Gas

What is the unit of standard entropy?

J•K^-1•mol^-1

How does temperature affect entropy?

The greater temperature particles have more energy and move more. Thus the arrangement of particles become more random.

More random arrangement = Higher entropy

When a solid ionic lattice is dissolved in solution what happens to entropy?

Entropy increases because the ions are more disordered.

How does change in number of gas molecules in a reaction affect entropy?

Increase in number of gas molecules = Increase in entropy

Decrease in number of gas molecules = Decrease in entropy

For a reaction to occur spontaneously ΔG must be positive or negative?

Negative

What are the limitations of the predictions of feasibility made by using ΔG?

● Reaction may have high activation energy

● Rate of reaction may be very slow