AP Chemistry
AP Chemistry Name ____________________________
Unit 7, Test Review Date ________________ Hour ____
The heating curve for a sample of pure ethanol is provided above. The temperature was recorded as a 50.0 g sample of solid ethanol was heated at a constant rate.
1. Which of the following explains why the slope of segment T is greater than the slope of segment R?
A) The specific heat capacity of gaseous ethanol is greater than the specific heat capacity of liquid ethanol.
B) The specific heat capacity of liquid ethanol is greater than the specific heat capacity of gaseous ethanol.
C) The heat of vaporization for ethanol is greater than the heat of fusion for ethanol.
D) The heat of fusion for ethanol is greater than the heat of vaporization for ethanol.
2. Which of the following explains why segment S is longer segment Q?
A) The specific heat capacity of gaseous ethanol is greater than the specific heat capacity of liquid ethanol.
B) The specific heat capacity of liquid ethanol is greater than the specific heat capacity of gaseous ethanol.
C) The heat of vaporization for ethanol is greater than the heat of fusion for ethanol.
D) The heat of fusion for ethanol is greater than the heat of vaporization for ethanol.
3. Aluminum metal can be recycled from scrap metal by melting the metal to evaporate impurities.
a. Calculate the amount of heat needed to purify 1.00 mole of Al originally at 298 K by
melting it. The melting point of Al is 933 K. The specific heat capacity is 0.89 J/g∙K, and the
heat of fusion of Al is 10.7 kJ/mol.
b. The equation for the overall process of extracting Al for Al2O3 is shown below. Which
requires less energy, recycling existing Al or extracting Al from Al2O3? Justify your answer
with a calculation.
Al2O3 (s) ( 2 Al (s) + 3/2 O2 (g) ΔH = 1675 kJ/molrxn
4. Use the reactions below to determine ΔH for this reaction: 3 C (s) + 4 H2 (g) ( C3H8 (g)
C (s) + O2 (g) ( CO2 (g) ΔH = -394 kJ
C3H8 (g) + 5 O2 (g) ( 3 CO2 (g) + 4 H2O (l) ΔH = -2220 kJ
H2 (g) + ½ O2 (g) ( H2O (l) ΔH = -286 kJ
5. Look at the overall equation that you solved for in problem 4.
a. What kind of reaction does this represent? How do you know?
b. Rewrite the equation with the ΔH included as part of the equation.
c. Determine the mass of carbon that must react to release 1750 kJ of energy.
d. Determine the amount of energy released when 16.7 grams of hydrogen gas react.
6. The specific heat of lead is 0.129 J/g∙°C. Determine the amount of heat needed to raise the temperature of 4.55 grams of lead from 12.5°C to 26.8°C.
7. The specific heat of copper is 0.0385 J/g∙°C. Determine the mass of a sample of copper if it takes 250. J of energy to raise the temperature from 14.8°C to 29.2°C.
8. The following table lists the ∆Hf for some iron oxides.
|Compound |∆Hf |
|FeO(s) |- 272.0 kJ/mol |
|Fe2O3(s) |- 824.2 kJ/mol |
|Fe3O4(s) |- 1118.4 kJ/mol |
FeO(s) + Fe2O3(s) ( Fe3O4(s)
a. Use the formation enthalpies to determine ΔH for the above reaction.
b. What does the sign of ΔH indicate about the relative strengths of the bonds of the reactants compared to the bonds of the products?
9. 30.0 grams of aluminum that is 365 K is placed into 30.0 grams of water that is 298 K. Will the resulting temperature be closer to 298 K, closer to 365 K, or right in the middle? Explain.
10. A combustion reaction is performed in a calorimeter containing 75.0 mL of distilled water. If the combustion of 0.155 grams of ethane, C2H6, causes the water to increase in temperature from 23.5°C to 49.2°C, determine the ΔH for the combustion reaction in kJ/molethane.
LO 5.3 The student can generate explanations or make predictions about the transfer of thermal energy between systems based on this transfer being due to a kinetic energy transfer between systems arising from molecular collisions.
LO 5.4 The student is able to use conservation of energy to relate the magnitudes of the energy changes occurring in two or more interacting systems, including identification of the systems, the type (heat versus work), or the direction of energy flow.
LO 5.5 The student is able to use conservation of energy to relate the magnitudes of the energy changes when two nonreacting substances are mixed or brought into contact with one another.
LO 5.6 The student is able to use calculations or estimations to relate energy changes associated with heating/cooling a substance to the heat capacity, relate energy changes associated with a phase transition to the enthalpy of fusion/vaporization, relate energy changes associated with a chemical reaction to the enthalpy of the reaction, and relate energy changes to PΔV work.
LO 5.7 The student is able to design and/or interpret the results of an experiment in which calorimetry is used to determine the change in enthalpy of a chemical process (heating/cooling, phase transition, or chemical reaction) at constant pressure.
LO 5.8 The student is able to draw qualitative and quantitative connections between the reaction enthalpy and the energies involved in the breaking and formation of chemical bonds.
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