What word describes changing from a gas to a liquid?
To get a sense for this, we can draw out what the molecules in a gas would look like as well as what the molecules in a liquid would look like. Notice that the molecules in the gas are very spread out far apart from one another. The molecules in this gas are unconnected to one another by chemical bonds. They are essentially completely free to move about in any direction.
Notice the difference between the molecules in the gas and the molecules in this liquid state. As a liquid, these molecules do share some chemical bonds. And just visually, we notice that they’re much closer together than they were as a gas.
It’s this fact the difference in spacing between molecules in a gas and in a liquid that gives us a clue to what word we’re searching for in this question. We could say that overall a liquid is a condensed form of a gas. That is, if we start with a gas and then take energy away from it, cooling it down, the molecules in the gas will lose energy, stop moving quite so quickly, and they’ll bunch closer and closer together.
When the gas is cooled enough that these molecules go through a phase transition from a gas to a liquid, that’s known as condensing. One way to remember this word is to recall that when we go from a gas to a liquid state of a given substance, the molecules in that substance get closer together; they condense.