A substance often undergoes a change in temperature when energy is transferred between it and its surroundings. There are situations, however, in which the transfer of energy does not result in a change in temperature. This is the case whenever the physical characteristics of the substance change from one form to another; such a change is commonly referred to as a phase change. Two common phase changes are from solid to liquid (melting) and from liquid to gas (boiling); another is a change in the crystalline structure of a solid.
All such phase changes involve a change in internal energy but no change in temperature. The increase in internal energy in boiling, for example, is represented by the breaking of bonds between molecules in the liquid state; this bond breaking allows the molecules to move farther apart in the gaseous state, with a corresponding increase in intermolecular potential energy.
If a quantity Q of energy transfer is required to change the phase of a mass m of a substance, the ratio { L = Q/m } characterizes an important thermal property of that substance. Because this added or removed energy does not result in a temperature change, the quantity L is called the latent heat (literally, the “hidden” heat) of the substance.
Latent heat of fusion Lf is the term used when the phase change is from solid to liquid.
Latent heat of vaporization Lv is the term used when the phase change is from liquid to gas.
Energy in itself has no color so what do we mean by 'green energy?' There seems to be no single or universal definition of 'green energy' but it has various interpretations. Is it called green because the color green is generally aligned with nature and so whatever is benign towards nature gets labeled 'green', in a rather generic way? ניטור לתחנות כח
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