Thermodynamics Lecture Notes

Overview of Enthalpy and Reactions

• In a constant pressure environment, change in enthalpy (ΔH) equals the heat added to the system.
• Exothermic Reactions:
  • ΔH < 0 (enthalpy decreases)
  • Heat is released; energy exits the system.
• Endothermic Reactions:
  • ΔH > 0 (enthalpy increases)
  • Energy is absorbed by the system.

Spontaneity of Reactions

• Spontaneity refers to a reaction occurring without external energy.
• Exothermic Reactions:
  • Often spontaneous as they release energy.
• Endothermic Reactions:
  • Less likely to be spontaneous as they require energy input.

Factors Affecting Reaction Spontaneity

1. Enthalpy (ΔH): Energy release increases spontaneity.
2. Entropy (ΔS): Increase in entropy (disorder) increases spontaneity.
3. Temperature (T):
   • High temperature can influence the direction of reaction.

Reaction Scenarios

• ΔH < 0 and ΔS > 0:
  • Likely spontaneous at any temperature.
• ΔH < 0 and ΔS < 0:
  • Spontaneous at low temperatures; high temperatures may not be spontaneous.
• Importance of Temperature:
  • At high temperatures, entropy becomes significant.
  • High kinetic energy can disrupt stable configurations.

Gibbs Free Energy (ΔG)

• Formula for spontaneity: [ ΔG = ΔH - TΔS ]
• If ΔG < 0, the reaction is spontaneous.
• Key Points:
  • Negative ΔH (energy release) and positive ΔS (increased disorder) favor spontaneity.
  • Temperature affects the weight of entropy in the equation.

Conclusion

• The change in Gibbs free energy (ΔG) predicts reaction spontaneity.
• Future discussions will cover the derivation of the Gibbs free energy formula from thermodynamic principles.