The specific latent heat of fusion of a substance is the amount of energy required to change one kilogram of a solid to liquid without changing the temperature For ‘m’ kilograms E = m Lf • Energy is measured in Joules • Mass is measured in kilograms • Specific latent heat is measured in J/kg

The specific latent heat of vaporisation of a material is the amount of energy required to change one kilogram of material from liquid to gas without a change of temperature For ‘m’ kilograms E = m Lv Energy is measured in Joules Mass is measured in kilograms Specific latent heat of vaporisation is measured in J/kg

A bath is filled with 60 kg of ice. Calculate the energy needed to melt all of the ice in the bath. The specific latent heat of fusion of water = 334, 000 J/kg. Energy absorbed = mass x specific latent heat Q = ml Q = 60 kg x 334, 000 J/kg Q = 20, 040, 000 J = 20. 0 MJ How much energy is needed to boil all the water in the bath and change its state to water vapour? The specific latent heat of vaporization of water is 2, 260, 000 J/kg. Q = ml Q = 60 kg x 2, 260, 000 J/kg Q = 135, 600, 000 J = 135. 6 MJ

Look at the values given for specific latent heat of fusion and specific latent heat of vaporisation. Why do you think that the specific latent heat of vaporisation is so much greater than the specific latent heat of fusion?