What is definition lateent heat?

Answer 1

Latent means hidden. Let us imagine that we have placed a container with water on a stove. A thermometer is inserted to note down the temperature now and then. As heat is handed over to the water in the container, its temperature rises. Say initially the temperature was 20 deg celcius. Now the temperature would go through 30, 40, 50, 60, 70, 80, 90, 95, 97, 98, 98.5, 98.9 and 100 deg. After 100 is reached though heat is continuously supplied, there won't be any rise thereafter. Now the question arises. Where does the heat go? The heat given is utilized not to rise the temperature but to covert each gram of water into vapour ie steam. Hence this heat is hidden and not sensed by the thermometer. So it is named as Latent heat of vapourisation.

Same way if we supply heat to an ice block with temperature -5 deg celcius, the temperature initially rises through -4, -3, -2, -1, -0.3, 0 deg celcius. After it reaches 0 deg, the temperature will be there itself. But heat is continuously given to the ice block. But no temperature rise. Here too the heat given is hidden and is used to melt every kilo gram of ice into water. Hence change of state. So Latent heat of melting or fusion of ice.