States of Matter
Matter itself exists in three PHYSICAL forms: solid, liquid, and gas. These are known as a substances physical state. Conversion among these phases are not chemical changes, as the chemical nature of the substance does not change. Don't be confused by the use of different terms to describe the same substance as it changes phases, it's still the same chemically. For example, we're familiar with water as being H2O in its liquid phase. But as you heat water up, it will change phases into the gas phase, but now be called steam. Steam is still water! If we look at our example reaction:
H2O (l) --> H2O (g)
we would say that water, in its liquid form, change to steam, the gaseous form of water. Changes of state are also known as a substance's phase. See this in action in the following hotspot.
|Scroll your mouse over the three beakers to learn more about the phase of matter that water can have.|
The two different terms (l & s) are used to indicate the phase the substance is in, in this example, water is going from being a solid to being a liquid (a change of state). A phase refers to having completely all solid, or all liquid or all gas. During a change of state or phase you will have a mixture of two phases. The phase a substance is in depends on the pressure surrounding the substance and its temperature. Chemists use graphs to display these effects visually.
|Scroll your mouse over the three different phases of water to learn more about the processes involved in these phase changes.