Thermochemistry and Thermodynamics

Thermochemistry and Thermodynamics

Thermodynamics is the study of energy and its transformations. For civil engineers, this is essential for understanding energy efficiency, phase changes, and the spontaneity of material degradation.

The Laws of Thermodynamics

1. First Law: Energy is conserved ($\Delta E = q + w$).
   • $q$: Heat added to the system.
   • $w$: Work done on the system.
2. Second Law: The entropy of the universe increases for spontaneous processes ($\Delta S_{univ} > 0$).
3. Third Law: The entropy of a perfect crystal at 0 K is zero.

Enthalpy ($\Delta H$)

Enthalpy is a measure of the total heat content of a system.

• Exothermic ($\Delta H < 0$): Heat is released (e.g., combustion).
• Endothermic ($\Delta H > 0$): Heat is absorbed (e.g., melting ice).

Entropy ($\Delta S$)

Entropy is a measure of disorder or randomness.

• Solids have low entropy; gases have high entropy.
• Spontaneous processes tend towards higher entropy.

Gibbs Free Energy ($\Delta G$)

The criterion for spontaneity at constant temperature and pressure. $\Delta G = \Delta H - T\Delta S$

• If $\Delta G < 0$, the reaction is spontaneous.
• If $\Delta G > 0$, the reaction is non-spontaneous.
• If $\Delta G = 0$, the system is at equilibrium.