10: Thermodynamics
- Page ID
- 518114
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- Keeping Energy in Check: The Thermodynamics Behind Safer Batteries
- 10.1: Spontaneity
- Spontaneous processes proceed without continuous input of energy under given conditions, while nonspontaneous processes require ongoing external energy. If a process is spontaneous in one direction under certain conditions, the reverse process is nonspontaneous under those same conditions. Spontaneity does not imply a fast rate of reaction. Although many spontaneous processes are exothermic, energy release alone does not determine spontaneity.
- 10.2: Entropy
- Entropy (S) is a state function that measures the dispersal of energy in a system and is related to the number of accessible microstates. A greater number of microstates corresponds to a more probable state and a higher entropy. Entropy increases with temperature, phase changes (solid → liquid → gas), molecular complexity, and mixing. Standard entropy changes can be calculated using tabulated standard molar entropy values.
- 10.3: The Second and Third Laws of Thermodynamics
- The Second Law of Thermodynamics states that spontaneous processes increase the total entropy of the universe. The Third Law of Thermodynamics states that a perfect crystal has zero entropy at absolute zero (0 K). This establishes an absolute scale for entropy, making it possible to calculate entropy changes using standard molar entropies. The standard entropy of a reaction can be calculated from the standard entropies of the reactants and products.
- 10.4: Free Energy
- Gibbs free energy (G) is a state function based solely on system properties and can be used to predict the spontaneity of a process. A negative value ΔG indicates that the reaction will proceed in the forward direction to reach equilibrium; a positive ΔG indicates that the reaction will proceed in the reverse direction; and a ΔG = 0 indicates that the system is at equilibrium. Several methods can be used to calculate free energy changes.
- 10.5: Free Energy, Equilibrium, and Non-Standard State Conditions
- Gibbs free energy change (ΔG) predicts the direction and extent of a reaction under any conditions. Standard free energy change applies under standard conditions and is related to the equilibrium constant (K) by the equation ΔG∘ = −RTlnK. The sign of ΔG indicates which direction the reaction proceeds to reach equilibrium, while its magnitude shows how far the system is from equilibrium. When Q=K, ΔG=0 and the system is at equilibrium.
- 10.6: Phase Transitions and Phase Diagrams
- Phase transitions involve changes in both enthalpy and entropy. Transitions that move particles apart absorb heat and increase entropy, while those that bring particles together release heat and decrease entropy. Vapour pressure increases with temperature and is higher for substances with weaker intermolecular forces. Heating and cooling curves show temperature changes as heat is added or removed. Phase diagrams map the stable phases of a substance at different temperatures and pressures.
- 10.E: Entropy and Free Energy (Exercises)
- The best way to check your understanding and build confidence is to work through the problems at the end of the chapter. If you have followed the explanations and worked through the examples, you should be able to solve them. Regular practice will reinforce what you have learned, deepen your grasp of thermodynamics concepts, and prepare you for assessments.