The Gibbs Phase Rule will be used extensively in the coming sections, so it is important that you understand it completely and utilize it effectively. Let's look at each of these variables in a little more detail. The number of components, C , is fairly straightforward. If I mix oil and water, I have two components. If I put some tin into molten lead, I have two components.
Water is an example of a one-component system.
If I put salt in water, I once again have two components. As you can see in the saltwater example, the number of phases, P , is something that is not always known. Sometimes this is the quantity we desire, but more often than not, we can determine the number of phases in a system by inspecting the system, either visually or with a microscope. If we keep in mind that a phase is a homogeneous region of matter, we can usually identify how many of these regions are present. Remember that these regions need not be continuous.