Lab: Molar Heat of Combustion of Fuel
Problem
Which fuel, methanol or ethanol, is better for heating water in a camping stove?
Prediction
Find the theoretical molar heat of combustion and energy per gram of fuel burned for methanol and
ethanol.
Design
Each fuel will be burned for two minutes and the temperature change of the water and the tin can will
be used in calculating the molar enthalpy of combustion of each fuel.
Procedure
1.
2.
3.
4.
5.
6.
7.
Measure the mass of the small tin can and record in table.
Assemble the tin can apparatus as shown on the board.
Measure 100.0 mL of water using a graduated cylinder and pour into the small tin can.
Measure the initial temperature of the water and record.
Measure the mass of the alcohol burner (with the cap) and record in table.
Ignite the burner and allow flame to heat tin can and water for two minutes.
Extinguish the flame by placing the cap on it with tongs and measure the final mass of the
alcohol burner.
8. Repeat step 3 to 7 for the other alcohol burner.
Evidence
Mass of tin can = 35.20g
Initial Mass of
Alcohol Burner
(g)
Final Mass of
Alcohol Burner
(g)
Initial H₂O(l)
Temperature (℃)
Final H₂O(l)
Temperature (℃)
Methanol
169.65g
167.60g
20.0℃
64.0℃
Ethanol
185.80g
184.20g
21.0℃
70.0℃
Analysis
Methanol
mcΔt
n
(0.100 kg)(4.18 kJ kg ⁻ ¹ K ⁻¹)( 44.0 K )+(0.0352 kg)(0.227 kJ kg ⁻ ¹ K ⁻ ¹)( 44.0 K)
ΔrHm=
mol
(2.05 g)(
)
32.04 g
ΔrHm=-292.9484031kJ mol ⁻¹
ΔrHm=-293kJ mol ⁻¹
ΔrHm=
ΔrH=
−293 kJ mol ⁻¹
32.04 g mol ⁻¹
This study source was downloaded by 100000755067623 from CourseHero.com on 01-12-2023 10:42:16 GMT -06:00
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ΔrH= -9.143208585kJ/g
ΔrH= -9.14kJ/g
Percent Error
−725.9 kJ mol ⁻¹−(−293 kJ mol ⁻¹)
x 100% = 59.6%
−725.9 kJ mol ⁻¹
Ethanol
mcΔt
n
(0.100 kg)(4.18 kJ kg ⁻ ¹ K ⁻¹)( 49.0 K )+(0.0352 kg)(0.227 kJ kg ⁻ ¹ K ⁻ ¹)( 49.0 K)
ΔrHm=
mol
(1.60 g)(
)
46.07 g
ΔrHm= -601.0271929kJ mol ⁻¹
ΔrHm= -601kJ mol ⁻¹
ΔrHm=
ΔrH=
−601kJ mol ⁻¹
46.07 g mol ⁻¹
ΔrH= -13.045956kJ/g
ΔrH= -13.0kJ/g
Percent Error
−1366.8 kJ mol ⁻ ¹−(−601 kJ mol ⁻ ¹)
x 100% = 56.0%
−1366.8 kJ mol ⁻¹
Conclusion and Evaluation
Ethanol is better for heating water in a camping stove because it releases more energy per
gram of ethanol burned. In this lab, our percent error for burning methanol was approximately 59.6%,
and our percent error for burning ethanol was approximately 56.0%, these percent errors could have
been caused by some of the errors that have occured in the lab. An example of an error in the lab was
that we did not ignite the burner immediately after taking the cap off, so some heat might’ve already
been lost, a way we can minimize the extent in which this error affects the final results of our lab is to
have one person take the cap off after the match has been lit and have the other person light it up
instead of only having one person do it. Another example of an error in this lab is that our
thermometer touched the tin can when measuring the temperature of the water, this could have
affected the result of our final temperature.
This study source was downloaded by 100000755067623 from CourseHero.com on 01-12-2023 10:42:16 GMT -06:00
https://www.coursehero.com/file/48579389/Lab-Molar-Heat-of-Combustion-of-Fueldocx/
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