SP2. Changes of state
By now you are probably well aware that all the matter around you exists in one of three states: it is a solid, like the earth; a liquid, like the water; or a gas, like the air. In some places on earth, however, materials are not restricted to one particular state, but can change from one to another depending on the weather. On a winter day Yellowstone Park, you might walk past a hot spring and see frozen ice and snow, liquid water, and clouds of steam all at once.
There are several different ways in which you could describe these three phases of matter. Solids have a definite shape, regardless of the container in which they are placed. A marble is still a marble, whether it is rolling around in a bowl or a flowerpot. Liquids take up the shapes of their containers; a liter of water could get round like a fishbowl or square like a brownie pan. Gases are harder to see and more difficult to imagine. They expand to take up the spaces in which they are placed. A gas will even escape from a container that does not have a tight lid on it, much like the carbon dioxide bubbles rise out of a can of soda once it has been opened.
Figure SP2.1. The three common states of matter.
- In the solid phase materials hold their shapes, like rocks.
- In the liquid phase, materials flow into new shapes to fit a container, like water.
- In the gas phase, materials expand in three dimensions to fill all available space, like air.
Another way of thinking about these states of matter has to do with the speed of the molecules in the matter, and how much energy those molecules contain. If you don't feel like you have much energy, you probably lay around a lot near the bottom of your container or dorm room, like a lump of coal on the bottom of a coal bin. If you have more energy, you might move around throughout your room, walking from place to place on the floor, but largely staying within its walls. If you have a great deal of energy, you may begin to dance or leap into the air or escape through the doorway to the outside.
- In the solid phase, particles of matter are packed closely together and moving very little.
- In the liquid phase, particles of matter are packed loosely together and moving more.
- In the gas phase, particles of matter are far apart from each other and moving freely.
Matter is a little bit like that, too. How much energy a group of molecules has -- and consequently how quickly they are moving on average -- strongly influences whether that material is in the solid, liquid or vapor phase. Solids tend to be composed of very slowly moving molecules while gases generally consist of speedier ones.
Problem SP2.1.
Draw a picture of a group of methane (CH4) molecules in the solid state, liquid state and phase.
Remember, each molecule has the same form whether it is in the gas phase, liquid phase or solid phase. The only thing that changes is the amount of energy the molecules have. As a result, the speed of the molecules and the ability of the molecules to attract each other also changes.
Figure SP2.2. Mobility of molecules in different states of matter.
This site was written by Chris P. Schaller, Ph.D., College of Saint Benedict / Saint John's University (retired) with other authors as noted on individual pages. It is freely available for educational use.
Structure & Reactivity in Organic, Biological and Inorganic Chemistry
by Chris Schaller is licensed under a
Creative Commons Attribution-NonCommercial 3.0 Unported License.
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