Which Alcohol, Ethanol or Methanol, Releases More Heat?
By: Vivian and Tracey
Introduction:
Rising environmental pollution caused by an abuse of fossil fuels has generated a
greater need and interest in alternative fuel sources. Two viable alternative fuels
are ethanol and methanol, which have the potential to alter the way our world
consumes energy by cutting down pollutants. In this experiment, we aim to find out
which of the two fuels, methanol or ethanol, releases the most energy and thus
would be better suitable as the new alternative fuel source of the future.
Necessary information for this experiment includes the specific heat capacities of
the two chemicals: 2.470 J/g K for ethanol and 2.545 J/g K for methanol.
Furthermore, the chemical formulas for ethanol and methanol are CH3CH2OH and
CH3OH. The molar mass of ethanol is about 46 g mol-1 and the molar mass of
methanol is about 32 g mol-1.
Background:
Ethanol is an alcohol, typically made in the United States from fermented corn or
organic materials such as paper. Ethanol is the alcohol found in many alcoholic
beverages, however the version used for motor fuel is not drinkable as there are
poisonous chemicals added to it. Methanol can also be made from biomass
resources, such as wood. Methanol is not drinkable in any form, and is very
poisonous if ingested. Both of these alcohols therefore are renewable resources, or
in other words fuels that can be replenished unlike gasoline or diesel, which can
only be produced after millions of years underground. Though there are many
positive aspects in using ethanol or methanol as an alternative fuel there are
however many downsides. Both Ethanol and Methanol have high percentages in
vehicle miles-per-gallon loss when traveling in comparison to gasoline, which is why
it is important to consider which alcohol produces more energy. The more energy
produced, the more efficient the alcohol is, which is what we are aiming to
determine in our experiment.
Question
Will methanol or ethanol produce a greater amount of heat energy when combusted?
Hypothesis
If the two fuels, ethanol and methanol, are burned, then ethanol will produce a
greater amount of heat because ethanol contains a greater number of covalent
bonds, meaning it has stronger bonds and thus contains a greater amount of energy
than methanol.
The Plan
Independent variable: the type of fuel burned (ethanol or methanol)
Dependent variable: The amount of heat produced
Controls: Same distance between flame and water, same can used to contain water,
same volume of water used, same amount of aluminum foil used to contain heat,
same amount of time burned
Materials:
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Distilled water (100 mL per fuel)
Aluminum foil
Soda (2x)
Spirit burner (2x – one ethanol, one methanol, 100 mL per)
Vernier temperature probe (1x)
LoggerPro
Ruler (1x)
A graduated cylinder (200 mL)
Ring stand
Stirring rod
Timer
Lighter
Scale
Clasp
Funnel
Diagram of materials:
Figure 1 shows a diagram of the setup used to measure the amount of heat released by a specific fuel
source (ethanol or methanol).
Procedure:
1.
2.
3.
4.
5.
Wrap both soda cans with aluminum foil.
Take one soda can and secure it inside the clasp.
Take the methanol and measure its mass on the scale.
Place the methanol in the center of the stand.
Take the clasp and secure it on the ring stand (use a ruler to ensure that the
soda can lies 4 cm above the methanol fuel).
6. Measure 100 mL of distilled water using a graduated cylinder and pour it
into the soda can using a funnel.
7. Set up LoggerPro and place the Vernier temperature probe into the water.
8. Using aluminum foil, create a heat containing cover and wrap it around the
methanol.
9. Press record on LoggerPro.
10. Take a lighter and light a flame on the wick connected to the methanol fuel.
11. Record the temperature change for 1 minute 30 seconds.
12. Measure the mass of the methanol.
13. Take the soda can that just finished burning and wrap new aluminum foil
around it.
14. Repeat steps 2-12.
15. Repeat steps 13-14.
16. Repeat steps 2-12 using ethanol.
17. Repeat steps 13 and 16 twice using ethanol.
Data Tables:
Chemical
Experimental Data
Mass before (g)
Mass after (g) (+/(+/- 0.001)
0.001)
Ethanol Trial #1
Ethanol Trial #2
Ethanol Trial #3
Methanol Trial #1
Methanol Trial #2
Methanol Trial #3
171.236
169.900
168.471
229.857
228.830
227.756
169.900
168.471
167.104
228.830
227.756
226.609
Temperature
Change (C) (+/0.1)
16.7
18.9
20.2
16.6
16.4
16.7
Figure 2 is a table containing the raw data of our experiment, which includes the mass of the ethanol and
methanol fuel sources and the temperature change in the reaction.
Ethanol
Methanol
Qualitative Observations
-Bigger flame
-Flame was much harder to control
-Very vibrant orange color
-Smaller flame
-Flame was much easier to control
-Less orange
Figure 3 shows the quantitative observations from the three trials involving methanol and ethanol.
Graphs:
The graphs below show the temperature change for both ethanol and methanol in
each of the trials. The time elapsed for all trials should be about 1:30 minutes.
Ethanol Trial 1:
Ethanol Trial 2:
Ethanol Trial 3:
Methanol Trial 1
Methanol Trial 2
Methanol Trial 3
Processed Data:
In order to find the amount of energy released, we will use the formula for heat,
which is as follows:
Q = mc∆T, where Q = heat released, m = mass of the water, c = 4.184 (specific
heat capacity of water) and ∆T = change in temperature.
Example of worked solution:
Q = mc∆T = (100)(4.184)(16.7) = 6987.28
Uncertainty: 0.05 (uncertainty of water’s mass) + 0.1 (uncertainty of
temperature) = 0.15
Example of worked solution for percent error:
[(accepted – experimental)/accepted] x 100 = [(1364 – 240.58)/1364] x 100
= 82.36%
Trial
Ethanol #1
Ethanol #2
Ethanol #3
Methanol #1
Methanol #2
Methanol #3
Heat released (J)
(+/- .15)
6987.28
7907.76
8451.68
6945.44
6861.76
6987.28
Heat released
(KJ/mol)
240.58
254.55
284.40
216.41
204.45
194.94
Percent of error
(%)
82.36
81.34
79.15
70.15
71.80
73.11
Figure 4 shows the total amount of heat released in each trial, which was found by processing the raw
data.
Worked example for ethanol: (6987.28 + 7907.76 + 8451.68)/3 = 7782.24
Ethanol
Methanol
Average Heat Released (J) (+/- .15)
7782.24
6931.49
Figure 5 shows the average heat released for ethanol and methanol in all three trials.
Conclusion:
From the results of our experiment, we can see that our hypothesis was supported
because ethanol produces more heat because it contains a greater number of
covalent bonds in comparison to methanol, meaning it creates more energy. We
found that when we burned ethanol and methanol, the independent variables, they
would make the water in the can increase in temperature, the dependent variable.
This relationship stayed consistent throughout all 6 trials of the alcohols. It
therefore can be inferred that both methanol and ethanol produce heat, as they both
increased the temperature of the water in the can. However, ethanol happened to
increase the temperature of the water more then methanol, meaning that ethanol
produces more heat.
This can be seen within each of our three trials as shown in Figure 4. First, in
relation to the first trial, ethanol produced a 6987.28 +/- .15 J of heat, which.
Comparatively, the first trial of methanol produced only 6945.44 +/- .15 J of heat, a
difference of about 41.84 Joules. This trial creates the smallest gap between the
amounts of heat released from ethanol and methanol. On the second trial involving
ethanol, the heat released was 7907.76 +/- .15 J, which is slightly larger than the
heat released in the first trial. The second trial of methanol released 6861.78 +/- .15
J of heat. Though the second trial did release a larger amount of heat than the
previous trial, the number is not significantly different from the first trial. The
difference between the second trials involving ethanol and methanol is 1045.98 J of
heat, which is a much larger difference between the two fuel sources than from the
first trial. Finally, in the third trial involving ethanol, the amount of heat released
was 8451.68 +/- .15 J, a number similar to the heat released in the second ethanol
trial. The third methanol trial released 6987.28 +/- .15 J of heat, which again does
not deviate much from the results of the previous two trials. Like in the first two
trials, ethanol releases more heat than methanol; this time it released 14.64.4 J
more.
In order to better compare the two fuel sources, we took the results of each of the
three trials and averaged the numbers based on fuel source. Thus, for ethanol,
Figure 5 shows the three trials average out to 7782.24 +/- .15 J of heat released. For
methanol, the three trials average out to 6931.49 +/- .15 J of heat released. From
this, we can see that ethanol released 850.75 J of heat more than methanol on
average. In terms of kilojoules per mole, ethanol also released a greater amount
each time (ethanol vs. methanol: 240.58 kJ/mol vs. 216.41 kJ/mol; 254.55 kJ/mol
vs. 204.45 kJ/mol; 284.40 kJ/mol vs. 194.94 kJ/mol). This is significant because it
shows the amount of heat released per mole, giving an indicator of the amount of
fuel needed to produce a specific amount of heat.
Evaluation:
From the conclusion of our experiment, we can see that ethanol produces more heat
than methanol and thus would make a better fuel source out of the two. A peculiar
thing about our experiment is the large percent error we encountered while
processing our data. We did not expect the number to be so high because we felt
that we took many necessary precautions to keep the heat from escaping, such as
building an aluminum cover to trap the heat inside. This may not have been enough,
as evidenced by the percent error, and thus we may have needed more equipment
to trap the heat inside. As shown in Figure 4, the trials involving ethanol yielded
percent errors of 82.36, 81.34, and 79.15. None of these numbers were even close
to the 1364 kJ/mol of heat that ethanol supposedly releases. Similarly, we received
high percent errors for methanol, which were 70.15, 71.80, and 73.11.
To better minimize the difference between the expected results and the actual
results of our experiment we need to better contain the heat given off the fuel
source to make sure it is only transferred to the water. First, rather than use an
aluminum cover, it may be more accurate to instead use another material that does
not absorb heat as easily as aluminum does. Another possibility would be to move
the heat source closer to the container of water.
References:
"Alternative Fuels and Advanced Vehicles Data Center: Ethanol." EERE: Alternative
Fuels and Advanced Vehicles Data Center Program Home Page. Web. 11 Feb.
2012. <http://www.afdc.energy.gov/afdc/ethanol/>.
"Alternative Fuels and Advanced Vehicles Data Center: Methanol." EERE: Alternative
Fuels and Advanced Vehicles Data Center Program Home Page. U.S
Department of Energy, 08 July 2011. Web. 11 Feb. 2012.
<http://www.afdc.energy.gov/afdc/fuels/methanol.html>.
"A Student's Guide to Alternative Fuel Vehicles - Ethanol and Methanol." Energy
Quest Room. Web. 11 Feb. 2012.
<http://www.energyquest.ca.gov/transportation/alcohols.html>.
"Basics of Heat Transfer." Water Cooling Systems, Pc Liquid Cooling Kit, Cpu, Video
Card, Hard Drive. Web. 11 Feb. 2012.
<http://www.koolance.com/technical/cooling101/002.html>.
"Ethanol Fuel: Journey to Forever." Journey to Forever: Hong Kong to Cape Town
Overland - An Adventure in Environment and Development, Join Us on the
Internet, All Welcome, Participation, Online Education, School Projects, Free
of Charge. Journey To Forever. Web. 11 Feb. 2012.
<http://journeytoforever.org/ethanol.html>.