Question

How dose the density of a liquid (or gas)vary with temperature how does the density of a liquid or gas vary with temperature

Answer 1

As the temperature of a liquid or gas is increased, the density will decrease and as the temperature is decreased, the density will decrease.

The causality for this is that when the temperature rises the molecules of a liquid or gas move faster and farther apart, occupying more space which then means that the substance will have a lower density. The opposite occurs for cooling (molecules slow down and move closer together occupying less space).

The same cannot be said for air, however. Temperature generally increases with air density. This can be witnessed with an increase in altitude; as one increases altitude, one witnesses a decrease in temperature, and simultaneously a decrease in air density and air pressure.