SPECIFIC LATENT HEAT
Objective n At the end of this lesson, you should be able to : n State that transfer of heat during a change of phase does not cause a change in temperature n Define specific latent heat n State that n Determine the specific latent heat of fusion and vaporisation n Solve problems involving specific latent
Introduction n The heat absorbed or the heat released at constant temperature during a change of phase is known as latent heat. n This transfer of heat does not causes a change in the kinetic energy of the molecules. n The four main changes of phase: n Melting n Boiling n Condensation n Solidification
n 3 common characteristics in the 4 processes of change of phase: A substance undergoes a change of phase at a particular temperature. n Heat energy is transferred during change of phase. n During change of phase the temperature remains constant even though there is transfer of heat. n n The amount of heat required to change the phase of substance depends on the mass and the type of material.
What is specific latent heat? n The specific latent heat of a substance is the amount of heat required to change the phase of 1 kg of the substance at a constant temperature.
The specific latent heat of fusion n Latent heat of fusion is the heat absorbed by a melting solid. n The specific latent heat of fusion of a substance is defined as the amount of heat required to change 1 kg of the substance from the solid to liquid phase without a change in temperature. n The amount of heat required to melt the ice is the same as the amount of heat release when solidifies to become ice.
The specific latent heat of vaporisation n Latent heat of vaporisation is the heat absorbed during boiling. n The specific latent heat of vaporisation of a substance is defined as the amount of heat required to change 1 kg of the substance from the liquid to gaseous phase without a change in temperature.
Example n 18 k. J of heat energy is required to convert 8. 0 g of water to steam at its boiling point. What is the specific latent heat of vaporisation of water? n lv = Q/m = 18 k. J / 0. 008 = 2. 25 x 106 J kg-1