What Happens to the Density When Liquids and Gases Are Heated?
We know now that the density of solids can change when certain conditions change. What about liquids and gases? Start by discussing liquids. Show students a bowl full or marbles and demonstrate how they roll around each other. Ask the students to visualize molecules heating up and bouncing off of each other. Ask the students to imagine that the marbles are bouncing off of each other. Show students a glass full of water filled to the top and sealed. What do they think would happen to the water if we heated it? [It would expand.] Note to Teacher: Students often bring up the issue of ice expanding as it freezes. Explain that water/ice is not a good example to reason from because it doesn’t follow all of the same rules as other liquids. When water freezes or crystallizes, it takes on a structure that incorporates little pockets of empty space, like a honeycomb. When the structure melts, the little pockets collapse and the liquid occupies less volume. The little pockets are full of vacuum,
