Condensed Practice Quiz - Thermochemistry
1. A 155.0 g sample of an unknown alloy is heated. When 1.25 kJ of heat is transferred to the metal, its temperature rises from
22.5ºC to 48.2ºC. Calculate the specific heat capacity (c) of this alloy in J/gºC.
2. A sample of fuel is burned in a bomb calorimeter. The heat capacity of the calorimeter and its contents (C) is 15.40 kJ/ºC. If the
temperature of the environment rises from 21.30ºC to 28.95ºC, calculate the enthalpy change (ΔH) for the reaction.
3. When 18.5 g of a salt is dissolved in a calorimeter, the temperature of the system falls from 25.0ºC to 17.45ºC. If the total heat
capacity of the calorimeter and solution is 1,150 J/ºC, calculate the molar enthalpy (ΔHx) in kJ/mol, assuming the salt has a molar
mass of 80.0 g/mol.
4. Given the following equation: 2H2S(g)+3O2(g) → 2SO2(g)+2H2O(g); ΔH= −1037 kJ. Write the modified thermochemical equation
and calculate the new ΔH for the reverse reaction scaled so that only 3/4 moles of O2 are produced.
5. Phosphorus(V) oxide is produced by: P4(s)+5O2(g) → P4O10(s); ΔH=−2940 kJ. Write the thermochemical equation for the reaction
that produces exactly 1.00 mole of O2(g) from the decomposition of P4O10(s). Include the new ΔH.
6. Given the ammonia combustion equation: 4NH3(g)+5O2(g) → 4NO(g)+6H2O(g); ΔH=−906 kJ. Calculate the ΔH for a reaction
where the equation is reversed and scaled such that the coefficient for H2O(g) is 1/2.
7. Using the reaction 2Al(s)+3Cl2(g) → 2AlCl3(s)+1408 kJ, calculate the total energy change (ΔH) when 1.50 kg of aluminum reacts
with excess chlorine. Express your answer in kJ and cite the molar mass used.
8. Consider the combustion of benzene: C6H6(l)+15/2O2(g) → 6CO2(g)+3H2O(l); ΔH=−3267 kJ/mol. Calculate the enthalpy change
per gram of benzene burned. You must show the use of the "denominator" from the balanced equation to find the molar enthalpy
first.
9. How many grams of nitrogen gas (N2) must react in the equation N2(g) + 3H2(g) → 2NH3(g)+91.8 kJ to release exactly 500 kJ of
heat? (Molar mass of N2=28.0 g/mol)
1. [2K] 2. [2K] 3. [2K]
4. [3K] 5. [3K] 6. [3K]
7. [3K] 8. [3K] 9. [4T]
1. A 155.0 g sample of an unknown alloy is heated. When 1.25 kJ of heat is transferred to the metal, its temperature rises from
22.5ºC to 48.2ºC. Calculate the specific heat capacity (c) of this alloy in J/gºC.
2. A sample of fuel is burned in a bomb calorimeter. The heat capacity of the calorimeter and its contents (C) is 15.40 kJ/ºC. If the
temperature of the environment rises from 21.30ºC to 28.95ºC, calculate the enthalpy change (ΔH) for the reaction.
3. When 18.5 g of a salt is dissolved in a calorimeter, the temperature of the system falls from 25.0ºC to 17.45ºC. If the total heat
capacity of the calorimeter and solution is 1,150 J/ºC, calculate the molar enthalpy (ΔHx) in kJ/mol, assuming the salt has a molar
mass of 80.0 g/mol.
4. Given the following equation: 2H2S(g)+3O2(g) → 2SO2(g)+2H2O(g); ΔH= −1037 kJ. Write the modified thermochemical equation
and calculate the new ΔH for the reverse reaction scaled so that only 3/4 moles of O2 are produced.
5. Phosphorus(V) oxide is produced by: P4(s)+5O2(g) → P4O10(s); ΔH=−2940 kJ. Write the thermochemical equation for the reaction
that produces exactly 1.00 mole of O2(g) from the decomposition of P4O10(s). Include the new ΔH.
6. Given the ammonia combustion equation: 4NH3(g)+5O2(g) → 4NO(g)+6H2O(g); ΔH=−906 kJ. Calculate the ΔH for a reaction
where the equation is reversed and scaled such that the coefficient for H2O(g) is 1/2.
7. Using the reaction 2Al(s)+3Cl2(g) → 2AlCl3(s)+1408 kJ, calculate the total energy change (ΔH) when 1.50 kg of aluminum reacts
with excess chlorine. Express your answer in kJ and cite the molar mass used.
8. Consider the combustion of benzene: C6H6(l)+15/2O2(g) → 6CO2(g)+3H2O(l); ΔH=−3267 kJ/mol. Calculate the enthalpy change
per gram of benzene burned. You must show the use of the "denominator" from the balanced equation to find the molar enthalpy
first.
9. How many grams of nitrogen gas (N2) must react in the equation N2(g) + 3H2(g) → 2NH3(g)+91.8 kJ to release exactly 500 kJ of
heat? (Molar mass of N2=28.0 g/mol)
1. [2K] 2. [2K] 3. [2K]
4. [3K] 5. [3K] 6. [3K]
7. [3K] 8. [3K] 9. [4T]
