Overview
The lecture focuses on entropy (S), how it changes with temperature and phase, and the general rules for predicting entropy changes in chemical and physical processes.
Entropy and Disorder
- Entropy (S) measures disorder in a system; higher disorder means higher entropy.
- As matter changes phase from solid to liquid to gas, entropy increases.
- Dissolving a solid into aqueous ions also increases entropy due to increased mixing and disorder.
Entropy and Temperature
- Entropy increases as temperature increases for all phases.
- The relationship between entropy and temperature is directly proportional: higher temperature, higher entropy.
- The increase in entropy (ΔS) for a given temperature change is greater at lower temperatures than at higher temperatures.
- ΔS is inversely proportional to temperature; the same heat added increases entropy more at lower temperature.
Phase Changes and Entropy
- There is a large jump in entropy during phase changes (e.g., solid to liquid).
- When heating a substance within the same phase, entropy increases gradually with temperature.
Practical Analogy and Implications
- Adding the same amount of heat to a cold object increases its entropy more than adding it to a hot object.
- Heat always transfers from hot to cold because it results in a net increase in total entropy, consistent with the second law of thermodynamics.
Key Terms & Definitions
- Entropy (S) — a thermodynamic property indicating the degree of disorder or randomness in a system.
- ΔS (Change in Entropy) — the difference in entropy between two states, influenced by temperature and phase changes.
- Second Law of Thermodynamics — states that the total entropy of an isolated system always increases in a spontaneous process.
Action Items / Next Steps
- Review rules for entropy changes with phase and temperature.
- Prepare for using these entropy relationships in future calculations.