Question

The heat energy obtained on burning 2 kg of hydrogen, coal, and petrol are given below:

Hydrogen- $3\times {10}^8$ J

Coal- $6\times {10}^7$ J

Petrol- $9\times {10}^7$ J

Arrange these fuels in the ascending order of their calorific values.

• A. Petrol < Hydrogen < Coal
• B. Petrol < Coal < Hydrogen
• C. Coal < Petrol < Hydrogen
• D. Hydrogen < Petrol < Coal

Answer 1

The correct option is C

Coal < Petrol < Hydrogen

Calorific value is the amount of heat liberated by the complete combustion of 1 kg of fuel. Its unit is kJ/kg.

The amount of heat liberated when 1 kg of hydrogen burns = $\frac{3\times {10}^8}{2}$

= $1.5\times {10}^8$ J/kg

= 150000 kJ/kg

The amount of heat liberated when 1 kg of coal burns = $\frac{6\times {10}^7}{2}$

= $3.0\times {10}^7$ J/kg

= 30000 kJ/kg

The amount of heat liberated when 1 kg of petrol burns = $\frac{9\times {10}^7}{2}$

= $4.5\times {10}^7$ J/kg

= 45000 kJ/kg

Arrangement of fuels in the ascending order will be- Coal < Petrol < Hydrogen