CHM170L Physical Chemistry 1 Laboratory
4th Quarter SY 2015-2016
Heat of Combustion
Marquez, Ariziel Ruth.1, (Nagayo, Juan Augustus A., Maquiling, Kenth Roger A., Martinez, Chelsea M., Ocado,
Patricia Andrea C.) 2
Professor, School of Chemical Engineering and Chemistry, Mapua Institute of Technology; 2Students, CHM170L/B41, School of Chemical Engineering, Chemistry and
Biotechnology, Mapua Institute of Technology
1
ABSTRACT
Heat of combustion is the amount of heat liberated after burning a specific substance that results to
breaking down into a simpler compound namely, CO2 and H2O. This experiment seeks to (i) familiarize
the calibration of bomb calorimeter, (ii) determine and compare the heat of combustion of a nonaromatic and an aromatic compound and (iii) to use calorimetry in studying compounds of differing
aromaticity. A bomb calorimeter was used to accurately determine the heat of combustion of benzoic
acid, naphthalene and sucrose. The obtained values of were 6359.498 cal/g, 9515.011 cal/g and
3956.569 cal/g respectively. The chemical reaction for combustion is typically that of a hydrocarbon
fuel reacting with oxygen derived from atmospheric air to form gaseous carbon dioxide, water vapor
and heat. These factors are molecular weight of the compound, number of carbons of the compound,
and Van der Waals forces. Most of the original error can be traced back to uncertainty in the quality of
the fits of the fore and afterdrift, as the original masses of sample and length of fuse wire both
contribute only minimally to the final error. Nevertheless, we received a fairly accurate measurement
with good precision, validating this experiment.
Keywords: Heat of combustion, Calorimetry, bomb calorimeter, Van der Waals forces
INTRODUCTION
MATERIALS
AND METHODS
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CHM170L Physical Chemistry 1 Laboratory
4th Quarter SY 2015-2016
RESULTS and DISCUSSIONS
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CHM170L Physical Chemistry 1 Laboratory
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The heat of combustion is the energy released
as heat when a substance undergoes complete
combustion with oxygen. Hence, it is associated
to the energy released in a certain compound
after breaking its bonds. The aromaticity of a
compound which can be determined by its
molecular
structure
affects
the
energy
increments.
benzoic acid. This observable difference can be
explained by the difference in number of aromatic
group and bond dissociation energy. Iron wire in
bomb calorimeter is used to initiate combustion by an
external electrical leads. If iron would be replace by
another wire, it must have specific heat capacity
comparable to the iron at 25C and that it should
completely combust at a range near to the samples.
Table 1. Heat of Combustion of Aromatic and
Non-Aromatic Compounds
It can also be inferred that the larger the number of
carbon atoms in the sample corresponds to larger
heat of combustion. This is indicated by the molar
masses of the compounds. Naphthalene has the
largest molar mass because it has the greatest
number of carbon atoms. This is because as the
number of Carbon atoms increases, the shape of the
molecule differs and it results to longer hydrocarbon
chain. As we move down the homologous group, a
spate CH3 molecule is being added in the chain.
Accordingly, the extra energy is required to break
apart this new molecule. It is much harder to break up
a longer hydrocarbon chain than a shorter one as
there are more bonds to break. Therefore, more
energy is required to break a longer hydrocarbon.
Moreover, we can also consider Van der Waals
forces, as the carbon atoms are added into the chain,
its mass increases. This will increase the Van der
Waals forces amidst the compounds, resulting to
stronger intermolecular forces of attraction. Therefore,
this leads to an increase in the enthalpy of
combustion of the compounds.
Sample
Mass, g
Measured
Benzoic
Acid
0.985
6359.49
of 8
combustion,
cal/g
Actual value
Percent Error
6317.49
0.66 %
Naphthalene Sucrose
0.498
9515.011
0.994
3956.569
9604.44
0.94 %
3940.32
0.41 %
Table 1 reveals the values obtained pertaining to the
heat of combustion of different compounds having
different aromaticity. These values were then
compared to their respective literature values.
Comparing the values to their literature values yields
very minimal percent errors, which proves the
success of carrying out the experiment. Relating the
results to aromaticity, it can be inferred that aromatic
compounds have higher heat of combustion than that
of non-aromatic compounds. The heat of combustion
differs in terms of the structure for aromatic
compounds. Higher heat of combustion can be
observed for compounds having more ringed
structure. Referring to the data, Naphthalene
exhibited the highest value of heat of combustion,
followed by Benzoic acid. Sucrose had the lowest
value of heat of combustion. Naphthalene and
benzoic acid both contain aromatic groups, described
by alternating single and double bonds ring formation,
which are more stable than cyclic alkanes contained
in sucrose. Higher heat of combustion is greater for
compounds having greater number of aromatic
groups. It is because more C=C bonds need to be
cleaved or broken to produce the products. On the
other hand, comparing naphthalene and benzoic acid,
naphthalene has heat of combustion higher than
Experiment 01 Group No. 7 June 15, 2016
CONCLUSIONS AND RECOMMENDATIONS
In this experiment, a bomb calorimeter was used and
successfully calibrated. Consequently, the values of
the heat of combustion of Benzoic acid, Naphthalene
and Sucrose were obtained, while accounting for
externalities like the vaporization of water or the PVwork that separates enthalpy from entropy. Our
calculated values of the heat of combustion of our
unknown sample, though not perfect, are far from
bad, with respectable percent errors of 0.66%, 0.94%
and 0.41% errors compared to their respective
literature values. To conclude, it can be inferred that
aromatic compounds have generally higher value of
heat of combustion. Also, compounds having more
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CHM170L Physical Chemistry 1 Laboratory
4th Quarter SY 2015-2016
carbon atoms have larger the enthalpy of combustion.
The reason is that the number of carbon atoms
increase, the molecules shape differs. The
hydrocarbon chain becomes longer. As we move
down the homologous group, a spate CH3 molecule
is being added into the alcohol chain. Thus, the extra
energy is required to break apart this new molecule. It
is much harder to break up a longer hydrocarbon
chain than a shorter one as there are more bonds to
break. Therefore, more energy is required to break a
longer hydrocarbon. This made naphthalene to have
the largest heat of combustion among the three
samples. This is due to the high energy released
during the breaking of bonds in this aromatic
compound. Having been able to efficiently perform the
experiment, it can be established that the objectives
of this experiment were successfully met.
http://www.infoplease.com/encyclopedia/science/heat
-combustion.html
[3] neutrum (2014). Heat of combustion. Retrieved
from:
https://neutrium.net/heat_transfer/heatof-combustion/
1. Atkins, P. W.; Physical Chemistry, 8th ed., W. H.
Freeman, New York, 1994
2. Castellan, Gilbert W. (1983). Physical Chemistry,
3rd Ed. Addison-Wesley.
3. Levine, Ira N. (2009) Physical Chemistry, 6th Ed.
McGraw-Hill, Boston.
4. Alvin R. Caparanga, John Ysrael G. Baluyut, Allan
N. Soriano; Physical Chemistry Laboratory Manual,
Part 1., Philippines, 2006, pp. 4-8
5. Moore, Walter J. (1972). Physical Chemistry, 4th
Ed. Prentice-Hall, New Jersey.
REFERENCES
[1] Wikipedia. Heat of Combustion. Retrieved from:
https://en.wikipedia.org/wiki/Heat_of_combustion
[2] infoplease (2000). Heat combustion. Retrieved
from:
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