Hot can

Hot food or beverages prepared without external heat

Termite reaction

Welding of railway tracks

Combustion of fuel

Used for cooking food

Gel pads

Relieves fever

Self cooling beverages

Beverages in cold cans without storing in refrigerators or using ice

Sorbet

The tongue feels cold when the sorbet is put in the mouth

Fuel Value

• Fuels are substances that burn in the air to produce heat energy.
• Each fuel has different heat of combustion.
• The unit for fuel value is \(\text{kJ g}^{−1}\).
• The fuel value can also be determined with the heat of combustion of substances.

Question

The heat of combustion of octane, \(C_8H_{18}\) is \(-5\,500 \text{ kJ mol}^{−1}\).

Calculate the fuel value of octane, \(C_8H_{18}\).

[Relative atomic mass: H = 1, C = 12]

Solution

Molar mass of octane, \(C_8H_{18}\).

\(=(8 \times 12)+(18 \times1)\\ =96+18\\ =114\text{ g mol}^{−1}\)

Complete combustion of 114 g of octane, \(C_8H_{18}\) releases 5 500 kJ of heat. 

Therefore, combustion of 1 g of octane, \(C_8H_{18}\) is as follows;

\(=\dfrac{5\,500 \text{ kJ mol}^{−1}}{114 \text{ g mol}^{−1}}\\ =48.2\text{ kJ g}^{−1}\)

The fuel value of octane, \(C_8H_{18}\) is \(48.2\text{ kJ g}^{−1}\).