Lesson 2: 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.

Also, be sure to turn in the lab report and do the online homework for this lesson.

Self Quiz Answers

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

    a. CO₂    b. H₂O₂     c. PbO₂      d. SO₂     e. SiO₂

   CO₂ is the only non-polar material listed and has the weakest
    intermolecular forces (Van der Waal's bonds)

2. In the circled portion of this heating curve, heat is being:
    a. absorbed to speed up molecules.
    b. absorbed to break bonds.
    c. released by molecules slowing down.
    d. released by molecules forming bonds.

3. The process occurring in the indicated liquid portion of this graph is called:
    a. fusion. 
    b. vaporization.
    c. condensation.
    d. crystallization.

4. About how much heat must be gained by 40 g of water to change its temperature from 17 C to 25 C?
    a. 5 cal         d. 1000 cal
    b. 8 cal         e. 5 kcal
    c. 300 cal

5. "Endothermic" means that heat is by the chemicals in question.
    a. absorbed     b. released

6. The heat of crystallization can be summarized as the amount of heat when one mole of a chemical .
    a. absorbed ... condenses          d. absorbed ... freezes
    b. absorbed ... melts                 e. released ... freezes
    c. released ... melts

7. The strongest bonding between particles (i.e., molecules, ions, atoms, etc.) is found in materials which are at room temperature.
    a. solids     b. liquids     c. gases

8. Alcohol evaporates more readily than water.
        Which has stronger intermolecular bonds?  water
        Which has higher vapor pressure?  alcohol

9. Calculate the heat of vaporization of a substance if it takes 400 calories to boil off 8.0 g of the liquid. (Be sure to include sign and units.)
        50 cal/g

10. Calculate the specific heat of a substance if removing 150 calories from 5.0 g of it changes the temperature from 75 C to 55 C. (Be sure to include units.)
        1.5 cal/g^oC

 

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