Entropy & Spontaneity

When is a reaction said to be spontaneous?

When the overall transformation leads to an increase in total entropy.

The reaction also occurs without the need for a continual input of energy

Define entropy

The distribution of available energy among particles

Define Gibbs Free Energy

It related the energy that can be obtained from a chemical reaction to the change in enthalpy, change in entropy and absolute temperature

When does entropy increase?

When there are more ways of distributing energy

When Gibbs Free Energy is positive, what does it say about the reaction?

The reaction is not spontaneous

When Gibbs Free Energy is negative, what does it say about the reaction?

The reaction is spontaneous

When Gibbs Free Energy is 0, what does it say about the reaction?

The system is at equilibrium and there is no net change.

What is the equation relating the Gibbs free energy to enthalpy change, temperature and entropy?

What are the factors affecting entropy?

1. Temperature

2. Change in phase

2. Change in phase (eg melting, evaporation)

3. Mixing of particles

4. Expansion of gas

5. Change in the no. of particles

6. Dissolution of ionic solid

Comparing a gas, solid and liquid under the same conditions, which entropy is the highest and which one is the lowest?

Highest: gas

lowest: solid

How does an increased temperature affect entropy?

As temperature increases, the average KE increases, which leads to more random motion and thus more ways to distribute energy among particles. This leads to an increase in entropy

how does an increase in the number of particles affect entropy?

An increase in the number of particles increase the number of ways to distribute energy in the system, thus increasing the entropy