Thermodynamics: Laws, Entropy & Free Energy
Thermodynamics deals with the energy changes accompanying chemical and physical processes. Understanding the interplay between Enthalpy ($H$), Entropy ($S$), and Gibbs Free Energy ($G$) is crucial for predicting reaction spontaneity.
1. First Law of Thermodynamics
Based on the law of conservation of energy, the First Law states that energy can neither be created nor destroyed. The mathematical formulation relates Internal Energy ($U$), Heat ($q$), and Work ($w$).
For gases: $\Delta n_g = n_p - n_r$
Sign Convention Cheat Sheet
- Heat ($q$): Positive if absorbed (+ve), Negative if released (-ve).
- Work ($w$): Positive if work is done on the system (compression), Negative if done by the system (expansion).
Figure: Comprehensive Mind Map of Thermodynamic Processes and Laws
2. Entropy & Second Law
The Second Law introduces Entropy ($S$), a measure of disorder. It states that the total entropy of the universe increases in any spontaneous process ($\Delta S_{\text{total}} > 0$).
Entropy Trends
- State: Gas > Liquid > Solid.
- Temperature: Entropy increases with temperature.
- Mixing: Mixing of gases or dissolving solids usually increases entropy.
3. Gibbs Free Energy ($\Delta G$)
Gibbs energy combines Enthalpy and Entropy to predict spontaneity at constant temperature and pressure.
Conditions for Spontaneity
| $\Delta H$ | $\Delta S$ | Spontaneity |
|---|---|---|
| -ve | +ve | Always Spontaneous |
| +ve | -ve | Non-Spontaneous |
| -ve | -ve | Spontaneous at Low T |
| +ve | +ve | Spontaneous at High T |
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