How much heat energy is necessary to raise the temperature of 5 kg of water from 20oC to 100oC ?

 Suppose, m= 5 kg and c= 1 kcal/ kg ^oC

Then, change in temperature Δ t = 100-20=80^oC

Energy to be supplied to water = energy gained by water = mass of water × specific heat of water × change in temperature of water

= m × c × Δ t

= 5 × 1 × 80 = 5 × 80

=400 kcal

Therefore, the heat required to raise the temperature of water = 400 kcal