WAEC Physics 2020 Paper

specific latent heat of vapourization is the amount of heat energy needed to change 1 kg of liquid to vapour without a temperature change. The heat absorbed by the liquid at the beginning of vapourization is $8 \times 10^{3}\, \mathrm{J}$ and heat absorbed after the change of stage is $53 \times 10^{3}\, \mathrm{J}$. therefore, the total heat energy needed to change the liquid completely to vapour is $Q = 53 \times 10^{3} - 8 \times 10^{3}\, \mathrm{J} = 45 \times 10^{3}\, \mathrm{J}$Recall, $Q = \mathrm{mL}$Where, $L =$ specific latent heat of vapourization$\; Q = \mathrm{mL}$$L = \frac{Q}{m} = \frac{45 \times 10^{3}}{0.02}$$L = 2.25 \times 10^{6}\, \mathrm{JKg}^{-1}$