Chemistry 4th Quarter

Thermodynamic Properties

  • Internal Energy (U): The total energy contained within a system, ranging from kinetic energy of particles to potential energy from molecular interactions.

  • Enthalpy (H): A measure of the total heat content of a system, defined as H = U + PV, where P is pressure and V is volume.

  • Entropy (S): A measure of the degree of disorder or randomness in a system. It quantifies the amount of energy in a physical system that is not available to do work.

  • Free Energy (G): The energy available to do work at constant temperature and pressure, defined by the formula G = H - TS.

Thomsen-Berthelot Principle

  • This principle states that during a chemical reaction, the heat of reaction is equal to the heat change when the products are converted back to the original reactants at a constant pressure. This emphasizes the relationship between heat transfer and enthalpy changes in reactions.

Second Law of Thermodynamics

  • This law states that the total entropy of an isolated system can never decrease over time, and is constant only in ideal cases where the system is in equilibrium. It implies that energy transformations are not 100% efficient, and some energy will always be lost as heat.

Gibbs Free Energy (G)

  • Gibbs Free Energy indicates the amount of energy available to do work during a process at constant temperature and pressure. It can be used to predict the direction of a reaction:

    • If ΔG < 0: the reaction proceeds spontaneously (exergonic).

    • If ΔG > 0: the reaction is non-spontaneous (endergonic).

    • If ΔG = 0: the system is at equilibrium.

  • The relationship of Gibbs Free Energy with enthalpy and entropy is given by the equation:
    \Delta G = \Delta H - T\Delta S
    .