1. Phase Change and Density
L.E.Q.: How does a substances density change when changing to a different state of matter?

2. What do you think?
On a piece of scratch paper write a hypothesis (if, then, because) for the following problem:
What happens to density as phase changes from gas to liquid to solid?
Compare your hypothesis with your partner. Are they the same or different? Whose do you think is correct?

3. Density and Phase Change
Remember that density is the MASS of matter divided by the VOLUME!
D = m/v
Which do you think takes up more space 100g of water or 100g of water vapor?
100g of water vapor
Remember that gases have their molecules more “spread” out and therefore takes up more space!

4. Calculate the density of water and water vapor
100g of water has a volume of 100 mL…What is the density?
D=m/v
D = 100g/100mL
D = 1g/mL
100g of water vapor has a volume of 120mL…What is the density?
D= 100g/120mL
D= 0.83 g/mL
Liquid has the higher density!

5. Liquid to Solid Phase Change
What do you think happens to density as a liquid changes to a solid? Why?
Which takes up more space 100g of liquid gold or 100g of solid gold? Why do you think this?
Remember: In a solid the molecules are more compact (takes up less space)

6. Calculate 100g of liquid gold has a volume of 6.5mL.
D=m/v
D=100g/6.5mL
D=15.4g/mL
100g of solid gold has a volume of 5.2mL
D=100g/5.2mL
D=19.3g/mL

7. In General….
In general what happens to density as we go from solid to liquid to gas?
As we go from solid to liquid to gas, density generally decreases (this is why gas floats on liquid and liquid floats on solid)

8. EXCEPTION What happens to water as it is frozen?
Why does ice float on water, why do soda cans crack in the freezer?
As water freezes it expands, making ice (solid) less dense than the liquid form!