Question

State whether entropy change is positive or negative in the following example: 

Vaporisation of a liquid

Answer 1

1. A system's disorder or variability is measured by its entropy (S). More molecular chaos is indicated by a higher entropy value. 
2. The process by which a liquid turns into a gas is called vaporisation. Liquid molecules acquire energy during this phase transition and separate, spreading into a greater volume as gas molecules.
3. Effect on Entropy: 
   1. Molecules are densely packed and have limited mobility in the liquid phase.
   2. Molecules in the gaseous phase are widely separated and free to go in any direction.
   3. Entropy rises during vaporisation because gases are more random and disordered than liquids. 
4. Since molecular disorder increases, the entropy change (ΔS) is positive for the vaporization of a liquid.