1. CH 13 Random Questions

2. Energy & Phase Changes Heat absorbed = endothermic Heat released = exothermic

3. Energy & Phase Changes Heat absorbed = endothermic Heat released = exothermic Classify each of the following phase changes as either exo- or endothermic Melting (do you heat the substance or cool it?) endothermic Freezing exothermic You must remove heat from a substance (cool it) to freeze it

4. Energy & Phase Changes Heat absorbed = endothermic Heat released = exothermic Classify each of the following phase changes as either exo- or endothermic Vaporizing endothermic Subliming endothermic

5. Energy & Phase Changes Heat absorbed = endothermic Heat released = exothermic Classify each of the following phase changes as either exo- or endothermic Deposition exothermic Condensation exothermic

6. A towel is soaked in water and then hung in front of a fan. Does the towel change temperature? Why ? Water evaporating is endothermic Heat energy is removed from the surroundings to cause the evaporation & the result is -- Cooling (or a drop in temperature)

7. What is the b.p. of ethyl alcohol at sea level? Ans: 78 o C At what atmospheric pressure would water boil at 50 o C? Ans: 120 mm Hg

8. How can a mixture of ethyl alcohol and water be separated? Since the alcohol has a lower boiling point than water the 2 liquids can be separated by DISTILLATION. See page 69 in the textbook.

9. What is the state of water at 95 o C and 0.5 atm? Gas or Vapor What happens if pressure is applied to ice at a temperature of 0 o C? The ice melts- this is how ice skates work!

10. Which intermolecular forces will cause different water molecules to be attracted to each other? Dispersion forces are always present between any pair of molecules. Dipole-Dipole forces since water is a permanent dipole. Hydrogen-Bonding since H is bonded to an oxygen atom with 2 lone pairs on it. Of these attractions, H-bonding is strongest and Dispersion is weakest.

11. These random questions may appear in various ways on the CH 13 Test. Students wishing to improve their test grade should also complete the CH 13 Review. Students who complete the CH 13 Review and submit it before taking the CH 13 Test can earn up to 5 bonus points on that test.

12. Good Luck on the Test!