Describe the entropy changes during vaporisation of a substance.

During vaporisation, the entropy of a substance increases as it changes from a more ordered state to a less ordered state.

In more detail, entropy is a measure of the disorder or randomness of a system. In the context of vaporisation, this refers to the transition of a substance from a liquid state to a gaseous state. In the liquid state, the particles of the substance are relatively close together and have a certain degree of order. However, when the substance vaporises, the particles spread out and move more freely, resulting in a more disordered and random system. This increase in disorder corresponds to an increase in entropy.

The increase in entropy during vaporisation can be explained by the second law of thermodynamics, which states that the total entropy of an isolated system can never decrease over time. In other words, the natural tendency of any isolated system is to maximise its entropy. Therefore, when a substance vaporises, it is following this natural tendency towards increased entropy.

The entropy change during vaporisation can be calculated using the formula ΔS = Qrev/T, where ΔS is the change in entropy, Qrev is the heat absorbed or released in a reversible process, and T is the absolute temperature. For vaporisation, Qrev is the heat of vaporisation of the substance, and T is the boiling point of the substance in Kelvin. This formula shows that the entropy change is directly proportional to the heat of vaporisation and inversely proportional to the boiling point.

In summary, the entropy of a substance increases during vaporisation due to the transition from a more ordered liquid state to a less ordered gaseous state. This increase in entropy is a natural process that follows the second law of thermodynamics, and it can be calculated using the formula ΔS = Qrev/T.