Unit A Review
- In a simple calorimetry experiment involving a burning candle and a can of water, the temperature of 100 mL of water increases from 16.4 °C to 25.2 °C when the candle is burned for several minutes. What is the enthalpy change?
- When 50 mL of 1.0 mol/L hydrochloric acid is neutralized completely by 75 mL of 1.0 mol/L sodium hydroxide in a polystyrene cup calorimeter, the temperature of the solution changes from 20.2 °C to 25.6 °C. Determine the enthalpy change that occurs in the chemical system.
- Predict the change in enthalpy due to the combustion of 10.0 g of propane (ΔrH= -2043.9 kJ/mol) used in a camp stove.
- Predict the enthalpy change due to the combustion of 10.0 g of butane (ΔrH= -2657.3 kJ/mol) in a camp heater.
- The combustion of 3.50 g of ethanol is used in a calorimeter to heat 3.63 L of water from 19.88°C to 26.18 °C. Determine the molar enthalpy of combustion of ethanol.
- 2.98 g of methanol was burned to raise the temperature of 650 g of water by 20.9 °C. Calculate the molar enthalpy of combustion of methanol.
- The ΔrH for decane (C10H22) is -6.72 MJ/mol. What mass of decane would have to be burned in order to raise the temperature of 500.0 mL of water from 20.0 °C to 55.0 °C?
- The standard enthalpy changes for the formation of aluminum oxide and iron(III) oxide are
1 2Al (s) + 32O2 (g) → Al2O3 (s) ΔH= -1657.7 kJ
2 2 Fe (s) + 32O2 (g) → Fe2O3 (s) ΔH= -824.2 kJ
Calculate the standard enthalpy of change for the following reaction:
Fe2O3 (s) + 2Al (s) → Al2O3 (s) + 2 Fe (s) ΔH= ?
- Use Hess’ Law to calculate the molar enthalpy of formation of butane from its elements.
1 C4H10 (g) + 132O2 (g) → 4CO2 (g)+ 5H2O (g) ΔH= -2657.4 kJ
2 C (s) + O2 (g) → CO2 (g) ΔH= -393.5 kJ
3 2H2 (g) + O2 (g) → 2H2O (g) ΔH= -493.6 kJ
- Methanol can be made from natural gas. Determine the molar enthalpy of synthesis of methanol.
CH4 (g) + H2O (l) → CH3OH (l)+ H2 (g) ΔH= -?
1 CO (g) + 3H2 (g) → CH4 (g) + H2O (l) ΔH= -249.9 kJ
2 2H2 (g) + CO (g) → CH3OH (l) ΔH= -128.7 kJ
- Predict the standard enthalpy change of the reaction used to produce ammonium nitrate.
NH3 (g) + HNO3 (l) → NH4NO3 (s) ΔH= ?
- Nitric acid is produce from ammonia by the Ostwald process. Predict the standard enthalpy change for each reaction in the process.
a) NH3 (g) + O2 (g) → NO (g) + H2O (g) ΔH= ?
b) NO (g) + O2 (g) → NO2 (g) ΔH= ?
c) NO2 (g) + H2O (l) → HNO3 (l) + NO (g) ΔH= ?
13. You are given a 70 g sample of each of the metals shown in the table below, all at 25.0 °C. You heat each metal under identical conditions. Which metal will be first to reach 30 °C? Which will be last? Explain.
Metal / Specific Heat Capacity (J/g°C)Platinum / 0.133
Titanium / 0.523
zinc / 0.388
14. Use the following data to determine an experimental value for the molar enthalpy of combustion for ethanol, C2H5OH (l):
Initial mass of alcohol burner = 47.39 g
Final mass of alchol burner = 47.19 g
Mass of aluminum can = 84.37 g
Mass of aluminum can and water = 239.36 g
Initial temperature of can and water = 15.7 °C
Final temperature of can and water = 18.3 °C
Calculate the molar enthalpy of combustion of ethanol.
15. The complete combustion of 1.00 mol of sucrose yields 5.65 x 103 kJ of energy. Write balanced thermochemical equation for the combustion of sucrose in an open system. Calculate the amount of energy that is released when 5.00 g of sucrose is burned? How much water (in grams) could be warmed by 5.0 °C when the 5.00 g of sucrose is completely burned?
16. Carbon monoxide reacts with hydrogen gas to produce a mixture of methane, carbon dioxide, and water This reaction is summarized below:
4CO (g) + 8H2 (g) → 3CH4 (g) +CO2 (g) + 2H2O (l)
Use the following thermochemical equations to determine the enthalpy change of the reaction.
1 C (s) + 2H2 (g) → CH4 (g) ∆H°=-74.8 kJ
2 CO (g) + 12O2 (g) → CO2 (g) ∆H°=-283.1 kJ
3 H2 (g) + 12O2 (g) → H2O (g) ∆H°=-241.8 kJ
4 C (s) + 12O2 (g) → CO (g) ∆H°=-110.5 kJ
5 H2O (l) → H2O (g) ∆H°=+44.0 kJ
17. Using standard enthalpies of formation, determine the enthalpy of reaction for each of the following reactions.
a. CaO (s) + CO2 (g) → CaCO3 (s)
b. C2H2 (s) + H2 (g) → C2H6 (g)
c. NH3 (g) + O2 (g) → NO (g) + H2O (g)
18. Determine the efficiency of a camp stove given the following data:
Mass of propane burned = 4.48 g
Mass of steel pot = 575.00 g
Mass of soup = 275.37 g
Initial temperature of soup & pot = 4.5 °C
Final temperature of soup & pot = 75.4 °C
Specific heat capacity of steel = 0.503 J/g°C
Specific heat capacity of soup = 3.57 J/g°C
Multiple Choice/Numerical Response
Use the following information to answer the next question.
2CH3OH (l) + 3O2 (g) → 2CO2 (g) + 4H2O (g) ΔH° = –1 275.8 kJ
1. The amount of methanol that must be burned to raise the temperature of 250.0 g of water from 20.0 °C to 35.0 °C is
a. 6.16 × 10–3 mol
b. 1.23 × 10–2 mol
c. 2.46 × 10–2 mol
d. 2.46 × 101 mol
Use the following information to answer the next question.Fuel Molar Enthalpy of Combustion
Methane –802.5 kJ/mol
Ethane –1 428.4 kJ/mol
Butane –2 657.3 kJ/mol
Octane –5 074.1 kJ/mol
2. An interpretation that applies to the data in the table above is that the greater the number of carbon atoms in a fossil fuel molecule, the
a. lower the energy stored in the molecule
b. greater the strength of each covalent bond
c. greater the energy released during combustion
d. lower the moles of oxygen required for complete combustion
3. If 44.7 kJ of energy is transferred when 1.65 g of ethanal, CH3CHO (l), is burned in a calorimeter, then the molar enthalpy of combustion of ethanal is
a. –1.67 kJ/mol
b. –2.71 × 101 kJ/mol
c. –7.38 × 101 kJ/mol
d. –1.19 × 103 kJ/mol
4. Which of the following equations represents the balanced chemical equation for the decomposition of water and the energy transfer during the reaction?
a. H2 (g) + 12O2 (g) → H2O (l) + 285.8 kJ
b. H2O (l) → H2 (g) + O2 (g) + 285.8 kJ
c. 2H2O (l) + 285.8 kJ → 2H2 (g) + O2 (g)
d. H2O (l) + 285.8 kJ → H2 (g) + 12O2 (g)
5. When used as a fuel in automobiles, ethanol burns more efficiently than fossil fuels. The balanced equation, including the appropriate enthalpy change for the combustion of ethanol, is
a. C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (g) ΔHº = +1 234.8 kJ
b. C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (g) ΔHº = –1 234.8 kJ
c. C2H5OH (l) → 2C (s) + 3H2 (g) + 12O2 (g) ΔHº = +277.6 kJ
d. C2H5OH (l) → 2C (s) + 3H2 (g) + 12O2 (g) ΔHº = –277.6 kJ
Use the following information to answer the next question.The combustion of sucrose can be represented by the following equation.
C12H22O11 (s) + 12O2 (g) → 12CO2 (g) + 11H2O (g) ΔHº = –5 155.7 kJ
If 1.00 g of sucrose reacts as represented by the equation above, then i of energy is ii the surroundings.
6. The statement above is completed by the information in row
Row / i / iia. / 15.1 kJ / absorbed from
b. / 15.1 kJ / released to
c. / 0.066 4 kJ / absorbed from
d. / 0.066 4 kJ / released to
Use the following information to answer the next two questions.
Disposable lighters contain butane gas which undergoes combustion, as represented by the following equation.
2C4H10 (g) + 13O2 (g) → 8CO2 (g) + 10H2O (g)
7. When used as a fuel in automobiles, butane burns more efficiently than fossil fuels. The molar enthalpy change for the combustion of butane, is
a. –2 657.3 kJ/mol
b. –2 877.3 kJ/mol
c. –5 314.6 kJ/mol
d. –5 754.6 kJ/mol
Use the following information to answer the next question.A student uses an aluminium calorimeter to determine the molar enthalpy of solution for solid ammonium nitrate. The student assumes that the calorimeter neither gains nor loses heat during the experiment; that the density and specific heat capacity for the final solution are the same as those of water; and that the mass of the final solution is 150.00 g. The data were collected and recorded in the following table.
Mass of aluminum calorimeter 25.45 g
Mass of aluminum calorimeter and contents 175.45 g
Mass of ammonium nitrate 1.68 g
Initial temperature of calorimeter and contents 22.30 ºC
Final temperature of calorimeter and contents 20.98 ºC
1. The molar enthalpy of solution for ammonium nitrate in the calorimetry experiment is ______kJ/mol.
8. One reason that could explain why dynamite releases a large quantity of energy when it explodes is that the reaction is
a. endothermic, and the products have more potential energy than the reactants
b. endothermic, and the reactants have more potential energy than the products
c. exothermic, and the products have more potential energy than the reactants
d. exothermic, and the reactants have more potential energy than the products
Use the following information to answer the next question.The energy barrier that must be overcome for the catalyzed forward reaction to occur is called the i , and in the diagram above, it is the difference between ii .
9. The statement above is completed by the information in row
Row / i / iia. / enthalpy change / I and II
b. / enthalpy change / I and III
c. / activation energy / I and II
d. / activation energy / I and III
Use the following information to answer the next question.
The energy changes that occur when propane undergoes combustion are primarily due to changes in i energy resulting from ii .
10. The statement above is completed by the information in row
Row / i / iia. / potential / a rearrangement of bonds
b. / potential / an increase in molecular motion
c. / kinetic / a rearrangement of bonds
d. / kinetic / an increase in molecular motion
Use the following information to answer the next question.
11. According to the diagram above, the enthalpy change for the combustion of 1.00 mol of methane gas is
a. endothermic and represented by a negative ΔH value
b. endothermic and represented by a positive ΔH value
c. exothermic and represented by a negative ΔH value
d. exothermic and represented by a positive ΔH value
12. If a hot tub contains 1.20 x 106 g of water, the amount of energy required to warm the water from 12.0 °C to 40.0 °C is
- 6.74 x 107 J
- 8.99 x 107 J
- 1.41 x 108 J
- 1.60 x 108 J
Use the following information to answer the next question.
The decomposition of hot potassium chlorate to solid potassium chloride and oxygen gas occurs at a faster rate in the presence of solid manganese (IV) oxide, as represented by the following equation.
2KClO3 (s) MnO2 (s) catalyst 2KCl (s) + 3O2 (g)
13. When manganese (IV) oxide is used as a catalyst, the enthalpy change for the decomposition of potassium chlorate
a. stays the same
b. becomes more exothermic
c. becomes more endothermic
d. changes from exothermic to endothermic
14. In most plants, solar energy, water and carbon dioxide react to form glucose. The reaction is represented by the following equation:
6CO2 (g) + 6H2O (l) + energy → C6H12O6 (l) +6O2 (g)
This reaction takes place in the process of
a. respiration
b. photosynthesis
c. redox and neutralization
d. combustion and respiration
Key:
1. -3.69 kJ
2. -2.8 kJ
3. -463 kJ
4. -457 kJ
5. -1.26 x 103 kJ/mol
6. -612 kJ/mol
7. 1.55 g
8. -833.5 kJ
9. -150.6 kJ/mol
10. 121.2 kJ/mol
11. -145.6 kJ
12. a) -104.6 kJ
b) -58.1 kJ
c) 169.8 kJ
13. platinum
14. -434 kJ/mol
15. -82.5 kJ, 3.9 kg
16. -747.6 kJ
17. a) -179.2 kJ
b) -311.4 kJ
c) -104.6 kJ
18. 43.5 %
Multiple Choice/ Numerical Response Section
1. C
2. C
3. D
4. D
5. B
6. B
7. A
NR 1:39.5 kJ/mol
8. D
9. C
10. A
11. C
12. C
13. A
14. B