Key Thermodynamic State Functions to Know for Physical Chemistry II

Thermodynamic state functions are key concepts in Physical Chemistry II, helping us understand energy changes in systems. They include internal energy, enthalpy, entropy, Gibbs free energy, Helmholtz free energy, pressure, volume, and temperature, each revealing insights into chemical processes.

1. Internal Energy (U)

   • Represents the total energy contained within a system, including kinetic and potential energy of particles.
   • Changes in internal energy (ΔU) are crucial for understanding heat transfer and work done in thermodynamic processes.
   • Governed by the first law of thermodynamics, which states that energy cannot be created or destroyed, only transformed.

2. Enthalpy (H)

   • Defined as H = U + PV, where P is pressure and V is volume; it accounts for the energy required to create space for a system.
   • Useful for processes occurring at constant pressure, such as chemical reactions in open systems.
   • Changes in enthalpy (ΔH) indicate heat absorbed or released during a reaction, aiding in thermodynamic calculations.

3. Entropy (S)

   • A measure of the disorder or randomness in a system; higher entropy indicates greater disorder.
   • The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time.
   • Changes in entropy (ΔS) help predict the spontaneity of processes; spontaneous processes increase the total entropy of the universe.

4. Gibbs Free Energy (G)

   • Defined as G = H - TS, where T is temperature and S is entropy; it combines enthalpy and entropy to determine spontaneity.
   • A negative change in Gibbs free energy (ΔG < 0) indicates a spontaneous process at constant temperature and pressure.
   • Essential for understanding chemical equilibria and phase transitions.

5. Helmholtz Free Energy (A)

   • Defined as A = U - TS; it is useful for processes occurring at constant temperature and volume.
   • A decrease in Helmholtz free energy (ΔA < 0) indicates a spontaneous process under these conditions.
   • Helps in analyzing systems where temperature is constant, such as in certain physical and chemical processes.

6. Pressure (P)

   • The force exerted per unit area by gas particles colliding with the walls of a container; a fundamental property of gases.
   • Influences the behavior of gases and liquids, affecting phase changes and reaction equilibria.
   • Related to other state functions through equations of state, such as the ideal gas law (PV = nRT).

7. Volume (V)

   • The amount of space occupied by a system; a critical parameter in defining the state of a system.
   • Changes in volume can affect pressure and temperature, influencing thermodynamic processes.
   • Volume is a key factor in calculating work done during expansion or compression of gases.

8. Temperature (T)

   • A measure of the average kinetic energy of particles in a system; it influences the direction and rate of chemical reactions.
   • Plays a crucial role in determining the state of matter (solid, liquid, gas) and phase transitions.
   • Temperature is essential for calculating other thermodynamic properties, such as Gibbs and Helmholtz free energy.