- Combustion is a reaction when a substance burns completely in the excess oxygen.
- Example, combustion of methane in excess of oxygen produces carbon dioxide and water.
CH4 + 2O2 → CO2 + 2H2O
- All fuel combustion are exothermic reactions.
Heat of CombustionThe Heat of Combustion of a substance is the heat energy released when 1 mole of the substance is completely burnt in excess oxygen in a standard condition
Finding Heat of CombustionFigure Below shows a simple method for obtaining an approximate value for the heat of combustion of a fuel.
The heat of combustion can be calculated by using the formula
- Use wind shield to block the air flow. This can reduce the heat loss to the surrounding.
- Do not use wire gauze, to reduce the heat loss.
- Copper container is used because copper is a good heat conductor,
- The flame must be put near the base of the container,
- The water is always stirred with the thermometer.
- The increase of water temperature is kept below 30°C to prevent over heating and energy loss to the surroundings,
- The fuel is weighed frequently to prevent condensation
Combustion of 1.71 g heptane (C7H16) in excees oxygen will relase 75kJ of heat.
[RAM: H = l; C = 12]
(a) Write the equation of the reaction.
Find the heat of combustion of heptane.
Relative molecular mass of heptane
= 7(12) + 16(1) = 100
Number of mole of heptane
Heat of Combustion