Does Density Depend On Temperature

Temperature Effects on Density

Density

Density is the mass of whatsoever material per unit volume. Gases e'er have much lower density than the condensed phases. Most materials accept a lower density of the liquid than the solid only this isn't always true. Water has a higher density in the liquid state than the solid, then water ice cubes float.

Within a detail phase, how does the density depend on temperature?

Remember that temperature is related to the boilerplate kinetic energy of the atoms or molecules within the substance. We know that, for gases, the volume is directly proportional to temperature by the equation PV=nRT.

Pure Water

The density of liquid h2o is approximately 1.0 chiliad/mL. The chart at right requite the density in kg/one thousandⁱⁱⁱ. Split past 10ⁱⁱⁱ to get the density in g/mL.

Let'due south wait at the density of water at 25 deg C and compare that to a college temperature, 80 deg C. The density decreases from 0.9970 g/mL to 0.9718 as it is heated. This makes sense considering, as heat is added to the liquid water, there is greater kinetic energy of the molecules and in that location are likewise more vibrations of the water molecules. Together these hateful that each H₂O unit in liquid water takes up more space as the temperature increases.

Nosotros meet the same trend in going from liquid water at 25 deg C (0.9970 g/mL) to liquid water at 4 deg C (0.99997 g/mL). Density increment as the temperature decreases.

Below 4 deg C, yet, the density decreases again. How can nosotros explain this?

Remember that liquid water and solid water accept the same network of bonds. Liquid water at 25 deg is so speedily breaking bonds between H₂O units and reforming them that extra water molecules get trapped inside the h2o lattice. This is the reason why liquid h2o is more dense than solid h2o.

The bonds in water break more slowly as temperature decreases and the structure tend to trap fewer extra water molecules. At low temperature, more of the water has the same lattice every bit ice.

Wikipedia, Water Density

It is possible to have liquid water at temperatures well below 0 deg C. Molecules in this supercooled water are free to motion. Bonds are made and broken. The long range structure is not perfect but the short range construction of supercooled h2o is very much like ice. Adding a crystal to supercooled water causes instantaneous water ice formation.

Other Pure Liquids

Pure ethanol, CH₃CH₂OH, is some other pure liquid. It is similar to water in that it is polar, with a permanent dipole moment, and forms hydrogen bonds with itself. Information technology doesn't have the same type of three-dimensional lattice that water has though.

The table at right has the density of ethanol from 3 deg to forty deg C in g/mL. We tin can see that the density decreases with temperature through this range. Dissimilar the situation with water, there is no maximum density point.

Most other pure liquids are similar ethanol in this respect.

Solutions show the typical behavior of the pure liquid with temperature but the density is also strongly affected by the quantity of dissolved material.