States of Matter

When a substance has reached the gaseous state, the particles are moving at relatively high speeds, and in straight lines, until they encounter other particles or some other barrier. The spaces between the particles are many times the size of the particles themselves. Generally, gas particles travel large distances through space before colliding with another particle or object. When colliding, although energy can be lost by one particle, it is gained by another and there is no net gain or loss of energy.

Because the particles are flying freely in the gaseous state, gases will fill whatever space is available to them. Thus, 100, 1000, or ten million particles of gas in a container spread out and fill the entire container.