Practice question · Sort into groups
Sort each change by what it does to the entropy of the system.
Groups: Entropy increases · Entropy decreases
- Ice melting to liquid water
- A solid dissolving in water
- Water vapour condensing to liquid
- A protein folding into one compact shape
- Two gas molecules combining into one
- A gas expanding into a vacuum
Hints
- Ask whether the particles gain or lose freedom of arrangement.
- Fewer gas molecules, or a single fixed conformation, means fewer accessible microstates.
Show the answer
Entropy increases: Ice melting to liquid water, A solid dissolving in water, A gas expanding into a vacuum
Entropy decreases: Water vapour condensing to liquid, A protein folding into one compact shape, Two gas molecules combining into one
Why
Melting, dissolving and expanding all increase the number of accessible arrangements. Condensing, folding into one shape, and reducing the count of gas molecules all restrict them, so entropy falls.
Practise Entropy and the Second Law
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