2. Suppose 23.00 g ammonium chloride (53.491 gmol) dissolves in \'water in a cal

Question

2. Suppose 23.00 g ammonium chloride (53.491 gmol) dissolves in 'water in a calorimeter to form 100.00 g of solution. The temperature decreases by 10.75°C. Calculate the AH of solution of NH.CI in kJ/mol. Assume the specific heats of the solution and of the empty calorimeter are 4.18 J/(g·°C) and 0.170 kJ/oC, respectively. NH,Cl (s) NH..(aq) + Cl"(aq) »-?kJ/mol 3. Benzoic acid is used to determine the heat capacity of bomb calorimeters because it can be obtained in pure form, and its energy of combustion is known very accurately (26.43 kJ/g). Determine the heat capacity of a calorimeter that showed a temperature increase of 8.199°C when 2.500 g of benzoic acid was combusted.

Explanation / Answer

Q2

mol of salt = mass/MW = 23/53.49146 = 0.42997

total mass = 100 g

dT = 10.75°C

Qsolution = Qwater +Qcal

Qwater = m*C*dT

Qcal = Ccal*dT

Qsolution = m*C*dT +  Ccal*dT = (100*4.18 + 170)*10.75 = 6321 J

Qrxn = -Qsoln = -6321 J

HRxn = Qrxn /n = -6321/0.42997

HRxn = -14701.02 J/mol

HRxn = -14.7 kJ/mol

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