Chapter 19: Chemical Thermodynamics

Overview

• Thermodynamics explains and predicts reaction directions.
• Relates to energy, work, heat, and enthalpy.
• Heat capacity and specific heat are essential concepts.

First Law of Thermodynamics

• Energy cannot be created or destroyed.
• Energy of the universe = Energy of system + Energy of surroundings.
• Systems:
  • Open: Exchange energy and material.
  • Closed: Exchange energy only.
  • Isolated: No exchange.

Energy Types

• Kinetic Energy: Depends on mass, speed, temperature.
• Potential Energy: Depends on distance, charge, dipole moment, electron number, and bond energy.

Internal Energy and Work

• Internal energy related to heat transfer and work.
• Formula: ΔE = q + w
• Enthalpy (H): Heat at constant pressure.
  • ΔH = ΔE + PΔV
  • Positive ΔH: Endothermic
  • Negative ΔH: Exothermic

Heat Capacity

• Heat Capacity: Energy to raise temp of substance by 1K.
• Specific Heat: Energy to raise temp of 1g of substance by 1K.

State Functions

• Independent of path taken.
• Includes internal energy, enthalpy, entropy, and free energy.

Hess's Law

• Total enthalpy change is the same regardless of reaction path.

Entropy and Second Law of Thermodynamics

• Entropy (S): Measure of randomness.
• Entropy of the universe increases in spontaneous processes.
• Boltzmann Equation: S = k lnW, where W is microstates.
• Clausius Equation: ΔS = q_rev/T

Gibbs Free Energy

• Determines reaction spontaneity.
• ΔG = ΔH - TΔS
  • ΔG < 0: Spontaneous
  • ΔG = 0: Equilibrium
  • ΔG > 0: Nonspontaneous

Temperature and Spontaneity

• Reactions can be enthalpy or entropy-driven depending on temperature.
• Standard Free Energy of Formation: Used to calculate ΔG under standard conditions.

Equilibrium Constant and Free Energy

• Relationship between equilibrium constant (K) and Gibbs free energy.
• ΔG = ΔG° + RT lnQ
  • If Q < K, reaction shifts right.
  • If Q > K, reaction shifts left.

Reversible and Irreversible Processes

• Reversible Process: Maximum work, system always in equilibrium.
• Irreversible Process: More common, involves entropy increase.
• Pathways like isothermal and adiabatic processes analyzed using P-V graphs.