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CHEM3860:002
Jonathan J. Grayczyk
Experiment 2: Heats of Combustion
Technical Report
Experiment Run: November 23, 2017
Report Submitted: December 8
th
, 2017
TA:
Badri
Bhattarai
Professor: Dr. Findsen

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Abstract
The heats of combustion and heat capacity for naphthalene and benzoic acid were
determined through the use of bomb calorimetry. Using an oxygen bomb calorimeter
the heat capacity for benzoic acid was determined to be 9.99
kJ
˚ C
. From this value,
the heat of combustion for naphthalene was determined to be -5211.8
kJ
mol
possessing 1.000% error when compared to literature values. With the percent error
being so low, the experiment is assumed successful.
Introduction
In this experiment, the relationship between the heat of combustion and internal energy will be
examined using bomb calorimetry. Being one of the oldest known scientific methods used to
measure energy transfer, this is often a practical procedure to be employed. In this method, the
device used to measure energy is called a calorimeter. In bomb calorimetry, the heat of
combustion for a compound can be determined by using a second known compound as a
standard.
Calorimeters are regularly enclosed by constant temperature water bath which prevent the heat
loss from the system to the surroundings. Due to the amount of heat loss being 0, we can
consider the calorimeter to be an adiabatic system. Because of this, we can assume that the
change in temperature of the water during combustion is equivalent to the total amount of energy
released by the combustion process.
In order to use this method of calculation, a substance with a known heat of combustion such as
benzoic acid must be in order to determine the constant of the calorimeter. The sample substance
is placed inside the bomb upon which in comes into contact with an ignition wire in a pressure of
around 20 atms. A known volume of water is placed in the bomb and the initial temperature
recorded and the bomb ignited which send an electrical current through the wire igniting the
substance. This causes the sample to combust and the temperature of the water to subsequently
rise.
We can them calculate the adiabatic temperature change using equation 1.

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ΔT – (T
f
– T
i
) –(
dT
dt
)
I
(t
d
-t
i
) –(
dT
dt
)
f
(t
f
-t
d
)
Equation 1
If we have the mass of the known combustible, we can then determine the heat capacity of it
with equation 2.
C
(S)
=
−
ΔE known
T
2
'
−
T
₁
'
Equation 2
Using the average heap capacity of the known substance we can then determine the heat capacity
of the calorimeter by equation 3:
U
known
= -Cv
cal
(T
f
-T
i
)
Equation 3
Knowing the relationship between the internal energy of a sysem and the heat of combustion we
can use equation 4.
∆U = ∆H-∆(pv)
Equation 4
If we treat all the products as ideal gases, we can then rewrite equation 4 as:
∆H=∆U + RT∆n
gas
This then affords us then enthalpy of combustion for a pure compound.