Question

How many pounds of coal would you have to burn to generate enough heat to boil a 15 l kettle?

Answer 1

Note that
The heating value of standard coal is about 30,080 kJ/kg
1 L of water has a mass of 1.0 kg

The mass of 15 L of water = 15 kg.
The latent heat of vaporization of water is about 2260 kJ/kg,
 The energy required to boil 15 L of water is
(2260 kJ/kg)*(15 kg) = 33900 kJ

The mass of coal required to provide this energy is
(33900 kJ)/(30080 kJ/kg) = 1.127 kg

Because 1 kg = 2.205 lb, the mass of coal required is
(1.127 kg)*(2.205 lb/kg) = 2.485 lb

Answer: 2.49 lb (nearest hundredth)