Question EXE.2.HL.TZ0.11
| Date | Example questions Example questions | Marks available | [Maximum mark: 6] | Reference code | EXE.2.HL.TZ0.11 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Deduce, Explain | Question number | 11 | Adapted from | N/A |
The particles of an ideal gas initially occupy one half of an isolated container, whose second half is initially empty. The gas is then allowed to expand freely into the second half. The diagram shows two configurations of the gas: the initial configuration A and configuration B, in which equal numbers of particles occupy each half of the container.
When a particle moves to a new position within the same half of the container, the microstate of the gas is considered unchanged. When a particle moves to the other half of the container, a new microstate is formed.
Explain why the gas in configuration B has a greater number of microstates than in A.
[3]
Configuration A has only one microstate ✓
In configuration B, pairs of particles can be swapped between the halves ✓
Every such change gives rise to a new microstate «so there is a large number of microstates in B» ✓
Deduce, with reference to entropy, that the expansion of the gas from the initial configuration A is irreversible.
[3]
The entropy of the gas is related to the number of microstates
OR
and ✓
Since , the entropy in configuration B is greater ✓
A process that results in an increase of entropy in an isolated system is irreversible ✓