What is Heat of Combustion and Why Should You Care?
The heat of combustion is the total energy released when a fuel undergoes complete combustion with oxygen. Understanding this helps you make informed decisions about fuel efficiency and environmental impact.
How to Calculate Heat of Combustion
The formula combines the lower heating value with the energy from water vaporization:
[HC = \text{LHV} + \text{Heat of Vaporization} \times \left( \frac{\text{Moles of Water Vaporized}}{\text{Moles of Fuel Combusted}} \right)]
Where:
- LHV (Lower Heating Value) is the energy released per mole of fuel without considering the heat in water vapor
- Heat of Vaporization is the energy required to convert water from liquid to gas
- Moles of Water Vaporized is the number of moles of water produced during combustion
- Moles of Fuel Combusted is the number of moles of fuel burned
Calculation Example
Given:
- Lower Heating Value (LHV): 350 kJ/mol
- Heat of Vaporization of water: 40.8 kJ/mol
- Moles of water vaporized: 3 moles
- Moles of fuel combusted: 1.5 moles
[HC = 350 + 40.8 \times \left( \frac{3}{1.5} \right)]
[HC = 350 + 40.8 \times 2]
[HC = 350 + 81.6 = 431.6 \text{ kJ/mol}]
The heat of combustion is 431.6 kJ/mol.