Why latent heat is needed to change substance from solid to liquid?

Answer 1

Latent heat is required to be input to turn a solid to a liquid, or a liquid to a gas, and the reverse is true the other way. Thus when water is evaporated to water vapor, a fixed amount of heat must be supplied per kg of water evaporated, and similarly when water vapor condenses, the same amount of heat per kg is released. You can look up values of latent heat per kg in reference tables for different substances.

Specific heat is not relevant to the phase change itself, as the phase change is isothermal (ie at a constant temperature). Specific heat is a way of defining for a substance how much heat is needed to change its temperature by one degree, relative to water which has a specific heat of 1, because we define the heat unit, calorie, as the heat required to raise 1 gram of water by 1 degC. Thus for other substances you take the specific heat (which will be quoted as a number relative to 1) and multiply by the change in temperature and the mass of substance to get the heat quantity in calories. Note that in SI units you will use kilograms rather than grams, the answer will then be in kilocalories which is a more useful quantity. In nutrition, when 'calories' are quoted, these are in fact kilocalories.

Answer 2

Latent heat is needed to change a substance from solid to liquid because it helps break the intermolecular forces holding the solid structure together. This energy is used to weaken the bonds between molecules and convert the substance from a solid state to a liquid state, without changing the temperature.

Answer 3

In any solid substance, there are chemical bonds between the atoms and molecules of which the substance is composed, that hold it together. In order to make this solid into a liquid, you have to break those bonds, and that requires energy, which is the latent heat.

Answer 4

Latent heat is the energy that is required to be put in to (or taken out of) a system of a certain mass, to make a change of state in the system.

It is defined as L = Q/M, where Q is the energy required and M the mass being heated.

Answer 5

yes, at melting point or boiling point. Latent heat is the heat where the temperature remains constant but there is a change in state. For example, when water boils, water continues to gain heat but the temperature remains constant. This is called the latent heat of vaporization.

Answer 6

to break the bonds between compounds as the matter of the solids are hardly packed...