Temperature and Density | Chapter 3: Density | Middle School Chemistry
Relationship between density, pressure, and temperature. • What happens to density if pressure increases? – Increases ρ ~ P. (Boyle's Law). • What happens to. Download scientific diagram | Relationship between temperature and density of liquid water. from publication: Enhanced modeling of moisture equilibrium and. Since PV = nRT the fractional increase in density, at constant pressure, is equal to minus the fractional change in temperature, for small.
Temperature Affects Density
Completely fill another baby food jar with very cold water and add 2 drops of blue food coloring. Stir the water in both jars so that the coloring is well-mixed in both. Place the cold water jar on a paper towel. Hold a water-resistant card over the top of the hot water jar.
While holding the card against the jar opening, carefully turn the jar upside down. With the card still in place, position the jar of hot water directly over the jar of cold water so that the tops line up exactly. Slowly and carefully remove the card so that the hot water jar sits directly on top of the cold water jar.
Expected results Although removing the card may result in a little mixing or spilling, the hot yellow water will remain in the top jar and the cold blue water will remain in the bottom jar. Why do you think the hot water stayed on top of the cold water? Students should realize that there is a density difference between hot and cold water. Hot water is less dense so it floats on the denser cold water.
Ask students to make a prediction: What might happen if you placed the cold blue water on top of the hot yellow water and then removed the card? Cold water on top Use the same procedure as above, but place the jar of cold water, upside down over the jar of hot water. Expected results The cold blue water will immediately fall into the hot yellow water causing mixing.
The water will quickly become green throughout. Why do you think the hot and cold water mixed when the cold water was placed on top? When the cold water is placed on top, the colors mix because the cold water is more dense and sinks in the hot water.
Below 4 deg C, however, the density decreases again. How can we explain this? Remember that liquid water and solid water have the same network of bonds. Liquid water at 25 deg is so rapidly breaking bonds between H2O units and reforming them that extra water molecules get trapped inside the water lattice.
This is the reason why liquid water is more dense than solid water. 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 as ice.
Water, density and temperature
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 move.
Bonds are made and broken. The long range structure is not perfect but the short range structure of supercooled water is very much like ice.
Adding a crystal to supercooled water causes instantaneous ice formation. It is similar to water in that it is polar, with a permanent dipole moment, and forms hydrogen bonds with itself.
It doesn't have the same type of 3-dimensional lattice that water has though. We can see that the density decreases with temperature through this range.