Answer. Heat can be given to a substance without raising its temperature,When a substance is changing its physical state[for eg from solid to liquid and liquid to gas ]. The heat energy which has to be supplied to change the state of substance is called its Latent Heat.

When water boils its temperature remains constant. It is because of latent heat. The heat given to the system is spared for phase transition of water. The heat given to the system is absorbed as latent heat.

so where does the heat go? The heat supplied is used up in changing the state of matter as it has to work against the force of attraction of molecules. When a liquid boils, it absorbs a type of heat called latent heat of vapourisation.

When a solid melts, its temperature remains the same because the heat energy supplied is utilised to break the bonds between the particles of matter. Therefore, the temperature of the solid does not change till all the solid melts.

When a solid melts or a liquid boils, the heat supplied is actually used to break the bond forces between the molecules and bring them apart till the body changes its state completely. Thus, the energy is transferred to the molecules as kinetic energy and the temperature of body remains constant in the process.

In the case of evaporation, the energy is absorbed by the substance, whereas in condensation heat is released by the substance. For example, as moist air is lifted and cooled, water vapor eventually condenses, which then allows for huge amounts of latent heat energy to be released, feeding the storm.

Remember that a phase change depends on the direction of the heat transfer. If heat transfers in, solids become liquids, and liquids become solids at the melting and boiling points, respectively. If heat transfers out, liquids solidify, and gases condense into liquids.

Form of latent heat where energy flow during the change of phase is from solid to liquid. The change is exothermic (the system releases energy) when the direction is from liquid to solid.

The energy that is changing during a phase change is potential energy. During a phase change, the heat added (PE increases) or released (PE decreases) will allow the molecules to move apart or come together. Heat absorbed causes the molecules to move farther apart by overcoming the intermolecular forces of attraction.

There are two phase changes where the heat energy is released: Condensation: When gas condenses to liquid the quantity of energy converted from chemical to heat is called the Heat of Vaporization or Δ Hvap . When a liquid becomes a solid (freeze), heat energy is generally lost (given off).

Deposition releases energy and is an exothermic phase change.

Since the surrounding environment is losing energy, it cools down. During the processes of condensation, freezing, and deposition, water releases energy. The energy released allows the water molecules to change their bonding pattern and transform to a lower energy state.

You add energy to the liquid water in order to get it to change phase. They require the addition of energy or heat. The reverse processes (freezing, condensation and deposition) are all exothermic processes. This means that they release heat.