# Unit 6: Gibbs Energy and Thermodynamics

Unit 6 Objectives

By the end of this unit, you will be able to:

• Describe the difference between thermodynamics and kinetics
• Describe the difference between spontaneous and non-spontaneous processes
• Define enthalpy and entropy
• Relate entropy and enthalpy to state changes for a substance
• Describe Gibbs Free Energy
• Calculate standard entropy changes for a reaction using standard molar entropies
• Calculate standard change in free energy for a reaction
• Relate equilibrium and free energy

• 6.1: Spontaneous and Nonspontaneous Processes
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.
• 6.2: Entropy and the Second Law of Thermodynamics
Entropy (S) is a state function whose value increases with an increase in the number of available microstates.For a given system, the greater the number of microstates, the higher the entropy. During a spontaneous process, the entropy of the universe increases.
• 6.3: Entropy Changes Associated with State Changes
under construction
• 6.4: Heat Transfer and Changes in the Entropy of the Surroundings
• 6.5: Gibbs 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.
• 6.6: Entropy Changes in Chemical Reactions
Changes in internal energy, that are not accompanied by a temperature change, might reflect changes in the entropy of the system.
• 6.7: Gibbs Energy Changes in Chemical Reactions
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.
• 6.8: Gibbs Energy Changers for Non-Standard States
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 ΔG° < 0, then K > 1, and products are favored over reactants. If ΔG° > 0, then K < 1, and reactants are favored over products. If ΔG° = 0, then K = 1, and the system is at equilibrium. We can use the measured equilibrium constant K at one temperature and ΔH° to estimate the equilibrium constant for a reaction at any other temperature.
• 6.9: Gibbs 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 ΔG° < 0, then K > 1, and products are favored over reactants. If ΔG° > 0, then K < 1, and reactants are favored over products. If ΔG° = 0, then K = 1, and the system is at equilibrium. We can use the measured equilibrium constant K at one temperature and ΔH° to estimate the equilibrium constant for a reaction at any other temperature.