Wrap-Up

In this lesson we studied solids and liquids - the condensed phases of matter. We learned to correlate some of their basic properties with the strength of the intermolecular bonding that holds their atoms or molecules together. We also learned how to do calculations involving amounts of heat energy and both temperature and phase changes, and in doing so we learned about both heat capacities and the latent heats (the heat of vaporization and the heat of fusion).

At this point you should review once more the objectives for this lesson to make sure you have mastered them all. If you have not already, try the Self Quiz for this lesson and check your answers against the key, found below.

Self Quiz

1. Which of the following chemicals has the lowest boiling point? Why?

a. CO₂

b. H₂O₂

c. PbO₂

d. SO₂

e. SiO₂

2. About how much heat must be gained by 40.0 g of water to change its temperature from 17 °C to 25 °C?

3. "Heat of fusion" refers to the amount of heat _____ when one mole of a chemical _____

4. The strongest bonding between particles (i.e., molecules, ions, atoms, etc.) is found in materials which are __________ at room temperature.

5. Alcohol evaporates more readily than water.

a. Which has stronger intermolecular forces?

b. Which has higher vapor pressure?

6. Calculate the heat of vaporization of a substance if it takes 1670 joules to boil off 8.0 g of the liquid. (Be sure to include sign and units.)

7. Calculate the heat capacity of a substance if removing 150 joules from 5.0 g of it changes the temperature from 75 °C to 55 °C. (Be sure to include units.)

8. What is the name for the phase change in which a gas becomes a solid directly?

Self Quiz Answers

1. Which of the following chemicals has the lowest boiling point? Why?

CO₂ because it has only dispersion forces, which are weaker than hydrogen bonds (H₂O₂) ionic bonds (PbO₂) dipole-dipole forces (SO₂) and network covalent bonds (SiO₂).

2. About how much heat must be gained by 40.0 g of water to change its temperature from 17 °C to 25 °C?

40.0 g * 4.184 J/g°C * 8 °C = 1300 J

3. "Heat of fusion" refers to the amount of heat _____ when one mole of a chemical _____

absorbed ... melts

4. The strongest bonding between particles (i.e., molecules, ions, atoms, etc.) is found in materials which are __________ at room temperature.

solid

5. Alcohol evaporates more readily than water.

a. Which has stronger intermolecular forces?

water

b. Which has higher vapor pressure?

alcohol

6. Calculate the heat of vaporization of a substance if it takes 1670 joules to boil off 8.0 g of the liquid. (Be sure to include sign and units.)

1670 J/8.0 g = 210 J/g (note, sometimes heat of vaporization will be in J/mol)

7. Calculate the heat capacity of a substance if removing 150 joules from 5.0 g of it changes the temperature from 75 °C to 55 °C. (Be sure to include units.)

150 J = 5.0 g * C * 20 °C C = 1.5 J/g°C

8. What is the name for the phase change in which a gas becomes a solid directly?

deposition