Latent Heat of Vaporization

Introduction :

Latent is a Latin word which means hidden. Latent heat is hidden heat, which a body absorbs or releases when it changes form one state to another.

Latent heat of vaporization of a substance is the amount of heat required to change one unit mass of that substance from liquid to gaseous state. During this process, the temperature of the substance remains constant. The heat absorbed in the process used to change the state of that substance from liquid to gaseous state. The heat energy increases the internal energy of the substance in form of change of state with no rise in temperature. A substance starts changing its state from liquid to gaseous state upon reaching its boiling point. When change of state starts taking place, the temperature of the liquid becomes constant at the boiling point. The heat absorbed there after used up in changing its state from liquid to gaseous state.

Latent Heat of Vaporization :

Similar to the latent heat of vaporization, there is latent heat of fusion. Just like the latent heat of vaporization, it is the heat required by a substance to change from solid to liquid state. In this case, also there is no rise in temperature when change of state takes place.

Latent Heat of Vaporization :

For a particular substance, Latent heat of vaporization per unit mass is more than its specific heat. For example, Latent heat of vaporization of water is 2260 J/g whereas its specific heat is just 4.2 J/g per degree centigrade rise in temperature. That is why burn caused by steam at 100 degree centigrade is more severe than burn caused by water at 100 degree centigrade.  Similarly, ice at zero degrees centigrade is cooler than water at zero degrees centigrade.

We can conclude one should be more cautions in burns caused be steam because latent heat of vaporization comes into play causing more severe burns.