9: Thermodynamics
- Page ID
- 164781
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- 9.1: Reaction Spontaneity
- Chemical and physical processes have a natural tendency to occur in one direction under certain conditions. A spontaneous process occurs without the need for a continual input of energy from some external source, while a nonspontaneous process requires such. Systems undergoing a spontaneous process may or may not experience a gain or loss of energy, but they will experience a change in the way matter and/or energy is distributed within the system.
- 9.2: The Second Law of Thermodynamics - Entropy
- Changes in internal energy, that are not accompanied by a temperature change, might reflect changes in the entropy of the system.
- 9.3: Entropy of Substances
- These forms of motion are ways in which the molecule can store energy. The greater the molecular motion of a system, the greater the number of possible microstates and the higher the entropy. A perfectly ordered system with only a single microstate available to it would have an entropy of zero. The only system that meets this criterion is a perfect crystal at a temperature of absolute zero (0 K), in which each component atom, molecule, or ion is fixed in place within a perfect crystal lattice.
- 9.4: Gibbs Free Energy
- We can predict whether a reaction will occur spontaneously by combining the entropy, enthalpy, and temperature of a system in a new state function called Gibbs free energy (G). The change in free energy (ΔG) is the difference between the heat released during a process and the heat released for the same process occurring in a reversible manner. If a system is at equilibrium, ΔG = 0. If the process is spontaneous, ΔG < 0. If the process is not spontaneous as written.
- 9.5: Free Energy and Equilibrium
- For a reversible process (with no external work), the change in free energy can be expressed in terms of volume, pressure, entropy, and temperature. If the products and reactants are in their standard states and ΔG° < 0, then K > 1, and products are favored over reactants at equilibrium. If ΔG° > 0, then K < 1, and reactants are favored over products at equilibrium. If ΔG° = 0, then K=1, and neither reactants nor products are favored at equilibrium. We can use the measured equilibrium constant