365 Days of Climate Awareness 29 - Phases of Matter

 

365 Days of Climate Awareness

29 - Phases of Matter

I'm going to do a dive into some real basics. Before discussing the most fundamental parts of the climate system: atmosphere, ocean, and cryosphere (ice): we need to review states of matter and water.

There are four phases of matter, and we're concerned with the first three: solids, liquids, gases; and plasma. Of these, liquids, gases and plasma are considered fluids, because the molecules can move in any direction, and are not fixed in place. Solids have the least heat (molecular) energy; next, liquids; then gases; then plasma. Moving from a lower energy state (i.e. solid to liquid, liquid to gas) requires a large input of heat. Moving from higher to lower (gas to liquid) releases heat.

Solids are defined as matter in which the atoms composing it remain in fixed positions with respect to one another. What we know as solid matter is mostly empty space (except in a neutron star, which is exceedingly dense), but the atoms do not move around freely. Chemical bonds of greater or less strength keep them in their positions. Of all phases of matter, solid has the least molecular energy.

A liquid is defined as matter in which molecules can move around with some freedom, but weak chemical bonds between the molecules keep them all at a roughly constant distance apart. For this reason a liquid will change its shape to fill a container (even if that is a floor, and the shape is a puddle), but its volume--the three-dimensional space it occupies--will not.

A gas is a fluid in which the molecules move with almost complete freedom, in any direction which their momentum dictates. Gases will expand to fill any available volume, as the molecules will not change direction unless they collide with other molecules. (Newton's second law: an object in motion will remain in motion unless acted on by an outside force.)

The force of gravity also traps gases to the earth--at least those of sufficient density. The earth has very likely lost a significant amount of atmospheric hydrogen to the solar system, as H₂ molecules bounce upward and are too light to be pulled back toward the planet. Like a rocket but on a far smaller scale, the H₂ molecules reach escape velocity and keep on moving out toward the stars. Just slowly.

Tomorrow: water molecules: more than you probably ever wanted to know.

Be well!