Chemical potential is a feature of materials that drives transformation. Where there is a difference in chemical potential between two parts of a system, change tends to occur, until the difference goes away.
Chemical potential takes its place among the core features of materials, alongside temperature, pressure, volume, mass, energy, and entropy. Each of these is a feature whose value can be measured for a particular material at a particular time. Chemical potential belongs to the same list, but it does extra work: it is the driver of change.
Materials change because of differences in chemical potential, the way water flows from a high reservoir to a low one. The differences may show up as concentration differences, as temperature differences, or as differences in arrangement, but the underlying shape is the same. Wherever the potential is unbalanced, the system tends toward balance; the act of moving toward balance is what we observe as a chemical reaction, a phase change, or any other transformation.
Chemical potential has a reputation for being one of the harder concepts in chemistry, partly because traditional treatments express it through dense mathematics. Treated as a measurable quantity rather than a derived abstraction, it becomes more tractable: a number we can in principle assign to a material, and a way of explaining why some materials change while others sit still. Where the potential is even, the materials are at rest. Where it is uneven, something is going to happen.
Question
Why do some materials sit while others change?
Reveal Merrill's answer →Hide answer
Because some materials, in their current arrangement, are at a balance of chemical potential, and others are not. Where the potential is even, things sit. Where it is uneven, the unevenness drives the transformation toward balance. To predict whether something will change is to ask whether its chemical potential is at rest.