1. Haber Process (Industrial $NH_{3}$ Synthesis)

$\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -92\ \text{kJ/mol}$

• $\Delta H < 0$, $\Delta S < 0$ (Case 3): spontaneous at LOW temperature
• Industrially: 450°C (kinetic compromise), 200 atm (Le Chatelier)
• Thermodynamics says low T is better; kinetics says high T is faster

2. Refrigeration (Adiabatic Expansion)

• Working fluid expands adiabatically: $q = 0$, $w < 0$ (BY system)
• $\Delta U = w < 0$ → temperature drops (gas cools)
• Cold refrigerant absorbs heat from food compartment

3. Ice Packs (Endothermic Dissolution)

$\text{NH}_4\text{NO}_3(s) \rightarrow \text{NH}_4^+(aq) + \text{NO}_3^-(aq) \quad \Delta H > 0$

• Endothermic but spontaneous at room T (large positive $\Delta S$)
• Absorbs heat from surroundings → cooling effect

4. Combustion Engines

$\text{Octane} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \quad \Delta H < 0$

• Exothermic combustion → high T and P gas → expansion work
• Adiabatic expansion in cylinder: converts $\Delta U$ to mechanical work

5. Protein Folding (Biology)

• Protein folding: often $\Delta H < 0$ and $\Delta S < 0$ (ordered structure)
• Spontaneous at physiological temperature because $|\Delta H| > |T\Delta S|$
• Temperature-sensitive: proteins denature at high T when entropy term dominates