Calculations Involving Phase Changes

Name: _____________________________________ Prd: _____ Score: ______
Calculations Involving Phase Changes
1. What does the specific heat tell you about a substance?
2. The specific heat of water is 4.18kJ/g °C. What does this number mean?
The specific heat of several liquids are listed in the table to the right. Beakers
containing 100mL of each of these liquids were
Specific Heat
Liquid
placed into an oven at the same time. All the
(J/g °C)
liquids were removed a few minutes later, before
Acetone
2.15
any of the liquids started to boil.
Water
4.18
Methanol
2.51
Olive Oil
1.97
3. The temperature of the liquids after they were removed from the oven
were measured. Rank the liquids from lowest to highest temperature.
Lowest
Highest
Temp  ________  ________ ________ ________  Temp
a. Explain your reasoning for your rankings above in terms of the specific
heat of the liquid.
4. Rank the liquids above from weakest intermolecular forces to strongest.
Weakest
Strongest
IMF  ________  ________ ________ ________  IMF
a. Explain your reasoning for your rankings above in terms of the specific
heat of the liquid.
5. A polar bond forms between atoms that have ( very similar / very different
) electronegativities these atoms share electrons ( evenly / unevenly )
resulting in one atom having a slight ________________ charge and the
other atom have a slight ______________ charge. This type of molecule
tend to have ( weak / strong ) intermolecular forces. Explain your reasoning
below.
6. Rank the liquids above from least polar to most polar.
Least
Most
polar  ________  ________ ________ ________  polar
7. Dietrich has 56.0g of methanol and wants to heat it from 23.0°C to a
temperature of 65.0°C. How many joules of energy will this require?
8. Laina heats 265g of water over a campfire, heating the water from 20.0°C to
90.0°C. How much heat did the water absorb?
9. If Jordan has 25.5g of olive oil that is at room temperature, 22.0°C. He adds
156kJ of heat to the olive oil. What is the new temperature of the olive oil?
Enthalpies of Fusion and Vaporization
The table to the right has enthalpy of
vaporization and fusion for three
substances.
Substances
Water
Methanol
Acetone
Enthalpy of
Vaporization
(kJ/mol)
40.7
35.1
31.3
Enthalpy of
Fusion
(kJ/mol)
6.0
3.1
5.7
10. What does the Enthalpy of Fusion tell you?
11. What does the Enthalpy of Vaporization tell you?
12. How many joules of heat are required to melt 65.0g of ice that is at a
temperature of 0°C? (Hint: Don’t forget to calculate the number of moles first!)
13. How much heat has to be released released when 98.7g of steam at 100°C
condenses?
14. The Enthalpy of Vaporization is ( less than / similar to / greater than ) the
Enthalpy of Fusion. Explain this trend at the molecular level.
15. Below is a heating curve for Acetone. The melting point of acetone is 95.0°C and the boiling point is 56°C.
Temperature (°C)
150
100
50
0
-50
0
50
100
150
200
-100
-150
Time
Calculate the amount of energy that would be required to heat a frozen block of
acetone from -150.0°C to gaseous acetone at 150°C. The calculation should
take 5 distinct steps. Clearly show your work below.