in latent heat, since fusion and melting do not result into a temperature change, where does the energy go?

Answer 1

In thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a substance during a change of phase (i.e. solid, liquid, or gas), - also called a phase transition.

The term was introduced around 1750 by Joseph Black as derived from the Latin latere, to lie hidden. The term is now obsolete, replaced by "enthalpy of transformation".

Two latent heats (or enthalpies) are typically described: latent heat of fusion (melting), and latent heat of vaporization (boiling). The names describe the direction of heat flow from one phase to the next: solid → liquid → gas.

The change is endothermic, i.e. the system absorbs energy, when the change is from solid to liquid to gas. It is exothermic (the process releases energy) when it is in the opposite direction. For example, in the atmosphere, when a molecule of water evaporates from the surface of any body of water, energy is transported by the water molecule into a lower temperature air parcel that contains more water vapor than its surroundings. Because energy is needed to overcome the molecular forces of attraction between water particles, the process of transition from a parcel of water to a parcel of vapor requires the input of energy causing a drop in temperature in its surroundings. If the water vapor condenses back to a liquid or solid phase onto a surface, the latent energy absorbed during evaporation is released as sensible heat onto the surface. The large value of the enthalpy of condensation of water vapor is the reason that steam is a far more effective heating medium than boiling water, and is more hazardous.

http://en.wikipedia.org/wiki/Latent_heat

There is also 'sublimation; where the phase change is directly between the solid and vapor phases.

Basically, in 'layman terms', the energy input is used in rearranging the bonds between atoms, making them weaker as (mostly) the atoms sit further apart as the phases go from the vapor to the solid. When the phases go in the opposite direction, the heat 'comes out' as the reverse occurs.

Answer 2

Before explaining this one must have some idea about the structure of solids, liquids and gases
In the states of matter a solid object is characterized by its resistance to deformation and changes of volume. A solid has these properties :
• The atoms or molecules that comprise the solid are packed closely together.
• These constituent elements have fixed positions in space relative to each other. This accounts for the solid's rigidity. A crystal structure is a unique arrangement of atoms in a crystal. A crystal structure is composed of a unit cell, a set of atoms arranged in a particular way; which is periodically repeated in three dimensions .
If sufficient force is applied, either of these properties can be violated, causing permanent deformation.
Because any solid has some thermal energy, its atoms vibrate. However, this movement is very small, and cannot be observed or felt under ordinary conditions.
A liquid's shape is determined by the container it fills. That is to say, liquid particles are free to move within the volume, but they form a discrete surface that may not necessarily be the same as the vessel. The same cannot be said about a gas; it can also be considered a fluid, but it must conform to the shape of the closed container entirely.
In a gas the atoms or molecules constituting the matter basically move independently, (more freely than those in a solid or liquid) with no forces keeping them together or pushing them apart.
When a block of ice is heated its temperature is increased becoming less -ve and finally it reaches 0 degree celsius. Then it starts melting. Though we are supplying more and more heat energy the temperature will not rise from 0 degree till the complete ice is converted into liquid. On further heating again the temperature starts increasing. Though heat energy is supplied during the conversion process the temperature remains the same. We have seen that the molecules in a solid is closely packed and certain amount of enrgy is required to be used to pull the molecules apart.and make them free to move which is the characteristic property of liquid. This energy is 80 calories per gram of ice. As this energy is not seen in the form of temperature it is called "latent(hidden) heat of fusion of ice".
On further heating, the temperature of the water rises till 100 degree. Once it reaches 100 degree again there is a standstill of temperature. The water starts boiling ( and becomes steam). Till the complete water is converted into steam the temperature remains the same 100 degrees though energy is supplied. During this span of time the heat energy is utilised for converting the water into steam( for further separating the molecules for their free & random movement) of 100 degree. As this temperature is also not seen outside it is called latent heat of steam. This equal to 540 calories per gram of steam.

Answer 3

Latent heat does not give a rise in temperature, it is simply stored as motion in the molecules of the substance concerned and is given up as the substance then changes back to a liquid from a gas or from a liquid back to a solid

Answer 4

In the case of fusion, the energy is released as radiation. In melting the energy was used in the process of raising the heat. of the material to the melting point.

Answer 5

A good question. They go into separating nearby atoms or molecules. To melt a solid, you need to pull adjacent molecules in the crystal lattice apart. And because the particles in a gas are further apart than in a liquid, you need to do work on the atoms in a liquid to overcome their attractive forces when you vapourise it.

Answer 6

The best way to learn this is to find some knowledgable, thinking experts in physical chemistry and in thermodynamics, and have them argue the question. I suspect the energy goes into the breaking of the hydrogen bonds and dipole bonds. These bonds form because their presence permits a lower energy state.

Answer 7

The energy goes into disrupting the bonds which hold the atoms or molecules in the solid state - ie. into "freeing up" the particles.