Chemistry › Section P · Thermodynamics › Topic P.3
The second and third laws
A system's entropy can fall during a spontaneous change, as when water freezes on a cold night. The second law explains why: what always rises is the entropy of the system and its surroundings together. The third law then gives entropy a true zero, so every substance can be given an absolute entropy value.
In this topic
- The system is not the whole story
- The second law of thermodynamics
- Worked example: why heat flows from hot to cold
- Entropy change of the surroundings
- Worked example: will water freeze?
- The third law of thermodynamics
- Standard molar entropies
- Entropy changes for reactions
- Worked example: burning methane
- Common mistakes to avoid
- Key takeaways
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