JAMB Physics 2011 Paper

Concept:Steam causes more severe burns because it carries extra heat energy stored as latent heat of vaporization.Explanation:When water changes to steam at the same temperature, it absorbs a large amount of heat called the specific latent heat of vaporization.This value is $2.1 \times 10^6 \, \mathrm{J\,kg^{-1}}$.Heating unit mass of water from $0^\circ\mathrm{C}$ to $100^\circ\mathrm{C}$ requires:$$Q = mc\Delta\theta = 4200 \times 100 = 4.2 \times 10^5 \, \mathrm{J\,kg^{-1}}$$Steam therefore possesses much greater heat energy per unit mass than boiling water.When steam condenses on the skin, it releases its latent heat in addition to cooling to body temperature.This explains why steam burns are more severe.Answer:B. steam possesses greater heat energy per unit mass.