| Themes > Science > Physics > Thermodynamics > Laws of Thermodynamics Basic Significance > Primarily Condensed Phases > Phase Equilibria |
It is useful to review some basic concepts of phases before introducing the thermodynamics. A phase is a homogeneous region of matter. This region need not be continuous. The bubbles in a liquid/gas system represent one phase, even though the bubbles are separated from each other. But don't confuse a phase with a substance. An oil/water mixture is a good example of a two phase system (with two substances), but ice in water (one substance) is an equally valid two-phase system. Both phases of the same substance simply coexist at a specific temperature and pressure. This brings us to the concept of phase transformations, which we should all be familiar with. We will discuss phase transformations in more detail later, but it is helpful for our review to look at how a substance can transform from one phase to another, usually through the addition of heat. The diagram below shows the typical phase changes a pure substance will go through as heat is applied: |
| Here, +Hm is the latent heat of fusion (or melting, or crystallization, as the case may be) and +Hv the latent heat of vaporization. We will return to phase transformations later, but let's now see why these phases form in the first place and why each one is stable over such a wide range of temperatures. |
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