Chemical and Physical Changes

In Chemistry, there are two basic types of changes of a substance: Chemical and Physical.

A Physical change is a change that occurs without changing the basic identity of a substance. A good example of this would be the changes of water from it's liquid state, to it's solid state (Ice) or it's gaseous state (vapor). No matter which of these three forms water is in, it is still water. It retains it's chemical makeup. These changes are known as phase changes.

A Chemical change occurs when a substance becomes a new and completely different substance. An example of a chemical change is an object rusting.

Evidence of a Chemical Change

There is a simple way to figure out whether the evidence of change of a substance points to a Chemical or Physical change. The name for this way of analyzing the evidence is called EPOCH, an acronym.

E - Effervescence (bubbles/gives off gas)
P - Precipitate (solid crystals form)
O - Odor (change of smell is detected)
C - Color Change
H - Heat (reaction heats up or cools down)