Latent heat  
LATENT HEAT For example the latent heat of fusion of water, that is when ice melts to form liquid water, is about 334 joules per gram (J/g) or 6.0 kJmol^{1}. While the ice is absorbing energy and melting the temperature remains constant at 0^{o}C. This is clearly shown with a phasechange diagram. Depending on the phase change different terms apply. For example: Lets take one mol, or 18g, of solid water (ice) at 0^{o}C. Supplying this amount of water with 6.0 kJ of energy, which happens to be the latent heat of fusion of water, disrupts all the hydrogen bonds that hold the water molecules in a tight crystal lattice. 

Consider the graph on the right of the temperature of one mol of solid water (ice) as it has energy supplied to it. 1) What is the value of A? Solution 

Calculations involving latent heat The heat energy required for a state change is given by the formula as shown on the right. Now let's see hwo to use this formula in calculations. 1. Calculate the amount of heat energy, in kJ, required to evaporate 36.0g of water at 100^{o}C given the latent heat of vaporisation of water is 41.0 kJmol^{1}. Step 1 Find the mol of water. => 36.0 / 18.0 = 2.00 mol Step 2 find the energy => q = n X L => energy = 2.00 X 41.0 kJ = 82.0 kJ 