CHM
2045C Module Seven Sample Exam ANSWERS
Module
Seven Part F: Calorimeter Problems 5
points
Benzoic acid (C6H5COOH) is sometimes used as a standard to
determine the heat capacity of a bomb calorimeter (constant volume). The
calorimeter is an insulated containing with 1.20 kg of water. When 1.32
g of benzoic acid is burned in a calorimeter that is being calibrated , the temperature rises from 20.93 oC to 22.93 oC.
What is the heat capacity of the calorimeter? The heat of combustion of
benzoic acid (qv)
is -26.42 kJ/g
Solution: Read section 6.6 in
the text. In the lab we will do a coffee cup calorimeter lab, which is a
constant pressure calorimeter. This problem is a bomb calorimeter which is
constant volume which is explained on pages 259-260.
ΔT =
22.93-20.93 = 2.00 oC
qwater =
Cwater x mwater
x ΔT
qwater =
4.184 J/g oC x
1200 g x 2.00 oC =
10,042 J = 10.04 kJ
qrxn = m
benzoic acid x ΔHbenzoic
acid
qrxn =
1.32 g x - 26.42 kJ/g = 34.87 kJ
qbomb =
Cbomb
x ΔT
qbomb =
Cbomb
x 2.00 oC
qwater + qrxn +
qbomb =
0
10.04 kJ +
(2.00 oC)
Cbomb +
34.87 kJ = 0
(2.00 oC) Cbomb + 44.91 kJ = 0
Cbomb = -
22.46 kJ/ oC
On page 260 is Example 6.7 which
is another worked example. Try Exercise 6.10 on page 261 as a sample Part F
problem. Both constant volume and constant pressure problems are at the end of
the chapter #31-#42 on pages 273-4