Chemical Thermodynamics

Thermodynamics: Essential Concepts to Remember

1. Thermodynamic Systems:

• Open systems: exchange energy and matter with surroundings
• Closed systems: exchange only energy
• Isolated systems: no exchange of energy or matter

2. State Functions and Path Functions:

• State functions: values depend on the state of the system, not the path taken to reach that state
• Path functions: values depend on the specific path taken to change the state

3. The First Law of Thermodynamics:

• Energy is conserved within an isolated system

4. Enthalpy (H):

• H = U + PV; represents the total heat content of a system

5. Entropy (S):

• S = k ln W; measures the randomness or disorder in a system

6. The Second Law of Thermodynamics:

• The entropy of an isolated system always increases

7. Free Energy (G):

• G = H - TS; a measure of the spontaneity and equilibrium of a system

8. Equilibrium:

• G = minimum; a system reaches equilibrium when the free energy is minimized

9. Chemical Reactions and Spontaneity:

• A chemical reaction is spontaneous if it lowers the free energy of the system (ΔG< 0)

10. Standard State:

• A reference state defined for temperature, pressure, and concentration

11. Gibbs Free Energy Change (ΔG°):

• ΔG° = ΔH° - TΔS°; predicts the spontaneity of a reaction at standard state

12. Reaction Quotient (Q):

• Q represents the ratio of product concentrations to reactant concentrations at any point in a reaction

13. Equilibrium Constant (K):

• K is the value of Q at equilibrium conditions

14. Le Chatelier’s Principle:

• When a system encounters stress, it shifts equilibrium to counteract the change

15. Partial Pressure:

• Pressure exerted by a specific gas in a mixture of gases

16. Raoult’s Law:

• PTotal = P1 + P2 + … + Pn; partial pressure of each component in a mixture is proportional to its mole fraction

17. Henry’s Law:

• The partial pressure of a gas above a solution is proportional to the concentration of the gas in the solution

18. Colligative Properties:

• Properties that depend on the concentration of particles in a solution

19. Boiling Point Elevation:

• The boiling point of a solution increases with increasing concentration of solute

20. Freezing Point Depression:

• The freezing point of a solution decreases with increasing concentration of solute

21. Osmotic Pressure:

• The pressure required to prevent the flow of solvent across a semipermeable membrane

22. Electrochemical Cells:

• Galvanic cells: spontaneous reactions produce electrical energy
• Electrolytic cells: electrical energy is used to drive nonspontaneous reactions

23. Standard Reduction Potential:

• Measure of the tendency of a half-reaction to undergo reduction

24. Nernst Equation:

• Relates the cell potential of an electrochemical cell to its standard reduction potential and the concentrations of reactants and products.