🔥 Thermodynamics

1. Basic Concepts

System: The part of the universe under observation.
Surroundings: Everything else in the universe.
State Functions: Properties whose values depend only on the initial and final states of the system, not the path taken (e.g., Temperature, Pressure, Volume, Internal Energy, Enthalpy, Entropy). Heat and Work are path functions.
Extensive Properties: Depend on quantity of matter (e.g., Mass, Volume, Enthalpy).
Intensive Properties: Independent of quantity of matter (e.g., Temperature, Density, Pressure).

2. First Law of Thermodynamics

Energy can neither be created nor destroyed. The total energy of an isolated system is constant.

ΔU = q + w Change in internal energy = Heat added to system + Work done ON the system.

3. Enthalpy (H) and Heat Capacity

Enthalpy (H): Total heat content of the system at constant pressure. H = U + PV. Change in enthalpy ΔH = ΔU + pΔV.

Heat Capacity (C): Heat required to raise temperature by 1°C. q = C × ΔT. At constant pressure (Cp) and constant volume (Cv), the relation is Cp - Cv = R.

4. Thermochemical Equations and Hess's Law

⚖️ Hess's Law of Constant Heat Summation

If a reaction takes place in several steps, then its standard reaction enthalpy is the sum of the standard enthalpies of the intermediate reactions into which the overall reaction may be divided at the same temperature.

5. Spontaneity and Entropy (S)

Entropy: Measure of the degree of randomness or disorder in the system. Solid < Liquid < Gas. For a spontaneous process in an isolated system, the change in entropy is positive (ΔS > 0).

6. Gibbs Energy (G)

Combines enthalpy and entropy to predict spontaneity.

ΔG = ΔH - TΔS (Gibbs-Helmholtz Equation)

Criteria for Spontaneity

If ΔG < 0, the process is spontaneous.

If ΔG > 0, the process is non-spontaneous.

If ΔG = 0, the system is at equilibrium.