Calorimetry Problems
1. When 12.29 g of finely divided brass (60% Cu, 40% Zn) at 95.0oC is quickly stirred into
40.00 g of water at 22.0oC in a calorimeter, the water temperature rises to 24.0oC. Find the
specific heat of brass.
Hints:
• The heat lost by the brass is gained by the surroundings (the water plus the calorimeter). What relation
can you therefore write between qbrass and qsurr?
• Since no information is given about the heat capacity of the calorimeter, you should assume it is
negligible.
• The final temperature of the brass is the same as the final temperature of the water. The specific heat of
water, c(H2O), is 4.184 J g-1 oC-1.
Answers: qsurr = q(H2O) = 334.7 J; qbrass = - 334.7 J; cbrass = 0.38 J g-1 oC-1.
2. In an experiment, 400 mL of 0.600 M HNO3(aq) is mixed with 400 mL of 0.300 M
Ba(OH)2(aq) in a constant-pressure calorimeter having a heat capacity of 387 J/oC. The
initial temperature of both solutions is the same at 18.88oC, and the final temperature of
the mixed solution is 22.49oC. Calculate the heat of neutralization in kJ per mole of HNO3.
Hints:
 The heat evolved in the neutralization reaction is gained by the surroundings (the mixed solution plus the
calorimeter). What relation can you therefore write between qrxn and qsurr?
 There are two contributions to qsurr. What are they? What assumptions (if any) need to be made in
calculating these contributions?
 Is this a limiting reagent problem, or are reactants supplied in the stoichiometric ratio given by the
equation? (Why do we care about this?)
 We want our answer in kJ per mole of HNO3. How do we calculate that?
Answers
oC;
qsolution = 12083.4 J; qcalorimeter = 1397.1 J; qsurr = 13481 J; qrxn = - 13481 J;
neut(kJ/mol
HNO3) = - 56.2 kJ/ mol HNO3.
3. When 1.00 dm3 of 1.00 mol dm-3 Ba(NO3)2 solution at 25.0C is mixed with 1.00 dm3 of
1.00 mol dm-3 Na2SO4 solution at 25.0C in a calorimeter, the white solid BaSO4 forms and
the temperature of the mixture increases to 28.1C. Assuming that the calorimeter absorbs
only a negligible quantity of heat, that the specific heat capacity of the solution is 4.18 J/Cg, and that the density of the final solution is 1.0 g/cm3, calculate the enthalpy changer per
mole of BaSO4 formed.
(25.9 kJ/mol)
4. In a coffee-cup calorimeter, 1.60 g of NH4NO3 is mixed with 75.0 g of water at an initial
temperature of 25.00C. After dissolution of the salt, the final temperature of the
calorimeter contents is 23.34C. Assuming the solution has a heat capacity of 4.18 J/C-g
and assuming no heat loss to the calorimeter, calculate the enthalpy change for the
dissolution of NH4NO3 in units of kJ/mol.
(26.0 kJ/mol)