Chemical thermodynamics

Introduction to Chemical Thermodynamics

Study of energy changes (heat, work) during chemical and physical processes

Deals with:

System: part under study

Surroundings: everything else

Types of systems:

Open (mass + energy exchange)

Closed (only energy exchange)

Isolated (no exchange)

Focuses on initial and final states, not the path

Important Terminologies

State function: depends only on state (e.g., U, H, S)

Path function: depends on path (e.g., heat q, work w)

Internal energy (U): total energy of system

Heat (q): energy transfer due to temperature difference

Work (w): energy transfer due to force

Extensive properties: depend on mass (volume, energy)

Intensive properties: independent of mass (temperature, pressure)

Zeroth Law of Thermodynamics

If A = B and B = C, then A = C (thermal equilibrium)

Basis for temperature measurement

Defines the concept of temperature

First Law of Thermodynamics

Law of energy conservation

Formula: ΔU=q−w

Energy cannot be created or destroyed

Only converted from one form to another

Isolated system → ΔU = 0

Cyclic process → ΔU = 0

Enthalpy (H)

Defined as: H=U+PV

At constant pressure: ΔH=qp

Exothermic (ΔH < 0 → heat released)

Endothermic (ΔH > 0 → heat absorbed)

Heat Capacity

Amount of heat required to raise temperature

C (heat capacity)

Cp (constant pressure)

Cv (constant volume)

Relation: C=q/ΔT

Applications of First Law

Calorimetry → measuring heat changes

Expansion work: w=−PΔV

Ideal gas processes

Helps calculate:

Internal energy changes

Heat exchanged

Work done

Second Law of Thermodynamics

Introduces entropy (S)

Heat flows from hot → cold

No process is 100% efficient

Entropy: Measure of disorder/randomness

ΔS=qrev/T

Spontaneous processes → increase in entropy

Carnot Cycle

Ideal reversible engine

Consists of:

Isothermal expansion

Adiabatic expansion

Isothermal compression

Adiabatic compression

Efficiency: η=1−(Tc/Th)

No real engine is more efficient than Carnot engine

Third Law of Thermodynamics

At absolute zero (0 K): Entropy of a perfect crystal = 0

Helps calculate absolute entropy values

Gibbs–Helmholtz Equation

Relates Gibbs free energy (G) with temperature

Predicts spontaneity of reactions

Key relation: ΔG=ΔH−TΔS

ΔG < 0 → spontaneous

ΔG > 0 → non-spontaneous

ΔG = 0 → equilibrium