explainthe role of energy in the process of phase changes.?

Answer 1

Put simply, during a change of phase (or state) energy put into a substance will increase its heat (but not its temperature). This heat energy will allow the bonds between molecules (or atoms) to break and allow them to move more freely.

In the example of solid to liquid, the substance starts of with very strong intermolecular bonds which, when heat energy increases are allowed to break down and allow the molecules to move about more freely as a liquid state (which is kind of like a square dance between molecules). You will notice now that the molecules have used this energy from the heat to increase their kinetic energy.

Once the phase change is complete the change in heat energy will now be continue to change the temperature of the substance.

Answer 2

You know what temperature is - it's a measure of how fast the molecules of a substance are moving. You can think of molecules in a solid like eggs in a box. They can move around a little bit, but beyond that any more energy you dump in there is going to have to go somewhere else. Thus, if you're putting energy into a material at a constant rate, you will usually see the temperature rise to a point, and then stop rising.

What happens with the energy instead is it's 'breaking the box' so to speak. Molecules are changed in state one by one to a new phase where they have more freedom of movement. And if the heat energy can move easily enough through the material, any attempt to increase the temperature is just going to end up being used to change state instead.

Of course, eventually everything will be in the new state. The molecules will have much more freedom of movement, and will be able to increase in temperature again, until they reach another limitation on their freedom (if there is one).

The same thing works in reverse, of course. If you are cooling something down (taking energy from it), you will see the temperature get lower and lower, then stop changing for a while as a phase change occurs, and then begin cooling again.

Most of the time there are also lots of subtle things going on as well. A gas takes up more volume than a liquid, so part of the energy cost of the phase change is going to involve pushing away any other things that happen to be in the way (or, if you push hard enough, you can often force something to change state without changing its temperature). And some materials don't conduct heat that well, so it's possible to have one phase, a surface where heat is being exchanged, and then another phase (in other words, if you toss an ice cube in a fire, it's not going to be quite as orderly as if you just left it on a counter).

Bottom line - energy must be absorbed or emitted from a substance for a phase change to occur!

Answer 3

Get 30 little kids(atoms/molecules) to sit close together in a playground on the floor. Give 'em loads of sugary drinks and food (the energy) and watch slowly as they begin to moce further and further apart, changing from a solid state and dissipating outwoardly, similarly like atoms/molecules in liquids and gases