Clint Heikkila Wood-to-Wheels Lesson 3
Measuring Energy Released by the Combustion of a Biofuel and a Fossil Fuel
Which fuel- ethanol or kerosene- will release the most energy when combusted?
Class: Chemistry / 11th Grade
Time: One Class Periods (50 minutes)
Location: Chemistry Lab
Learning Objectives- SWBAT:
Set up and conduct an experiment in which a fossil fuel (kerosene) and a biofuel (ethanol) are
combusted and perform calorimetry to compare the amount of energy released by each.
Michigan Content Standards:
C1.1CConduct scientific investigations using appropriate tools and techniques (e.g., selecting an
Instrumentthat measures the desired quantity–length, volume, weight, time interval).
C3.1cCalculate the ΔH for a chemical reaction using simple coffee cup calorimetry.
C5.7C Describe tests that can be used to distinguish an acid from a base.
C1.1EDescribe a reason for a given conclusion using evidence from an investigation.
Overview: In this lesson, the students will set up a simple aluminum can calorimeter and combust a sample of ethanol and a sample of kerosene in a glass, wick-type fuel burner. By taking the initial and final temperature measurements of a given amount of water being heated by the two fires, enthalpy calculations are made to determine the energy content of each fuel on a calorie per gram basis. The students, working in groups, will set up the calorimeter, measure and record all data, and perform all of the thermochemical calculations needed to make the final comparison between the two fuels.
This activity is also one of three in the lab kit called “Biofuels- Investigating Ethanol Production and Combustion” (the same kit used in Lesson 2 of this unit). Ordering information for this kit is as follows:
Supplier:Enasco
Lab Kit Title:Biofuels: Investigating Ethanol Production and Combustion Lab
Product Number:C29169M
Link:
Lesson Core
The Guiding Question: How does the amount of energy released by burning ethanol compare to the
amount of energy released by burning kerosene?
●Materials and Equipment Needed (per lab station):
(1) Lab kit- “Biofuels- Investigating Ethanol Production and Combustion”
*following is a list of needed materials that are not included in the kit
(1) ruler
(1) aluminum soda can
(1) ring stand
(1) ring stand clamp
(1) immersion thermometer
access to a mass balance
access to water
●Safety precautions: Review lab safety guidelines as pertaining to open flames (hair and loose clothing tied back, know location of fire extinguisher, etc). Students should wear safety glasses and be experts in the safe handling of flammable materials. Ensure that there is adequate ventilation in the room to prevent the accumulation of smoke and fumes.
●Advanced Preparation:
The students should be able to set up the calorimeter used in this lesson as well as measure out all needed amounts of materials. The teacher should ensure that all of the fuel burners have fuel in them and are in good working order prior to this activity.
The student guide that comes with the lab kit does a good job of going through the thermochemical calculations so not a lot of prior knowledge is required, but it would help if the students have an understanding of the concept of specific heat prior to beginning this activity.
●Engage: Prior to beginning the lab activity, ask the class to review how we “get our hands on” the energy we use to power cars. They should be able to track through the steps of converting the chemical potential energy stored in fuels to heat energy by burning the fuel, and converting the heat energy released in combustion to mechanical energy in an engine. This lab activity will focus on analyzing the chemical reaction of combustion and the conversion of stored energy to heat energy. Also discuss the concept of fuel-efficiency for car engines and point out that the more heat a burning fuel releases the more mechanical energy can be “made” from it. Finally, write the skeletal chemical equations for each combustion reaction on the white board and have the students balance them.
C2H5OH + 3O2 ------> 2CO2 + 3H2O + energy
ethanol
2C12H26 + 37O2 ------> 24CO2 + 26H2O + energy
ethanol
Before going into the lab, the students are asked to predict any differences they will find in the amounts of energy released from each combustion reaction. Explain that they will be calculating how much energy went into the water in the aluminum cans- all of their measurements will be based on this water. Assuming all of this energy comes from the fire, we can now tell how much energy the burning fuel gave off (it is an indirect measurement- energy cannot be measured directly, we can only measure the effect it has on something).
●Explore: Working in lab groups, the students will then set up the calorimeters and conduct the two reactions. Each fuel is burned three times for a total of six trials. A detailed procedure for this activity is included with the Lab Kit (copyright restrictions prevent the procedure from being detailed here). By the end of the lab procedure, each group should have all measurements needed to perform the enthalpy calculations. The Lab Kit provides data tables for recording all of these measurements and instructions for calculating the energy yields.
●Explain and Elaboration: This will be done in the lab reports they are to create for all three lab investigations. The students may not have time to complete all of the thermochemical calculations during this class period, but they should have all of the data needed to do so. The final “answers” should be calculated and included in the final lab report. Students should account for the following in their summaries for this activity:
-Which fuel released more energy per gram combusted?
-Show sample calculations for all values created from the measured data.
-What were your controls in this experiment?
-Identify potential sources of error that may have affected your results (how comfortable are
you with your results?)
-What would you do differently if you were to perform this investigation again?
-Kerosene is very similar to gasoline- what other information would you like to know before
deciding whether you would rather use ethanol or gasoline in your car?
●Evaluate and Lesson Closure:
If time permits, each group could share their results with the rest of the class. Follow this with the questions below to check for understanding of the calorimetry procedure. Remind the students to save all notes and handouts from this activity (including all data and calculations) as it will be part of a lab report they are to create at the end of the unit.
-Why was it important to know the specific heat of water in this experiment?
-Why was it important to measure the amount of water in the can?
-Why were temperature measurements made on the water and not on the “fires”?
-Would it be possible to get meaningful results if you put cooking oil instead of water in the
can?
-In what ways is an aluminum can a good choice for a calorimeter?
-In what ways is an aluminum can a poor choice for a calorimeter?
Lesson Extension
●Assessment Options: The class discussion at the end of the activity allows the teacher to assess the overall understanding of how calorimetry is done. Individually, this will be assessed with the lab report at the end of the unit.