Introduction: (Initial Observation)
We create heat energy by burning fuels. During the process of burning, chemical energy stored in fuels will be released in the form of heat. Since heat energy is what we are looking for, it is important to learn more about the amount of heat that we can get from different types of fuel. The amount of heat that you get from one pound of charcoal, probably is not the same as heat from one pound of natural gas or one pound of gasoline.
Knowing what fuel will create more energy can help us to put value on different fuels.
Although natural gas and heating oil are two common sources of heat energy in the winter, they are not our only choices. Electricity, liquid gases such as propane and butane, industrial alcohols such as methanol and ethanol are also among available fuels. Even some people burn wood or coal to warm up their homes. In the past, fat from animals and vegetable oils and bees wax have also been burned to create heat.
This project is an opportunity to compare the heat energy produced from different fuels.
The amount of heat released per unit mass or unit volume of a substance when the substance is completely burned is called heat of combustion.
In other words heat of combustion is heat released during combustion. In particular, it is the amount of heat released when a given amount (usually 1 mole) of a combustible pure substance is burned to form incombustible products (e.g., water and carbon dioxide); this amount of heat is a characteristic of the substance. Heats of combustion are used as a basis for comparing the heating value of fuels, since the fuel that produces the greater amount of heat for a given cost is the more economic. Heats of combustion are also used in comparing the stabilities of chemical compounds. For example, if equal quantities of two isomeric hydrocarbons burn to produce equal amounts of carbon dioxide and water, the one releasing more energy (i.e., with the higher heat of combustion) is the less stable, since it was the more energetic in its compounded form.
To see more information about energy and fuels, click here to see the informative attachment of this project.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
In this experiment, you will find and compare the heat of combustion of two or more different fuels such as paraffin wax and ethanol.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
The independent variable (also known as manipulating variable) is the fuel type. Possible values are Paraffin wax, Ethyl Alcohol, charcoal, etc. Actually any type of liquid or solid fuel may be tested, however, we are using paraffin wax and ethanol because they burn easy and do not create a lot of smoke.
The Dependent variable (also known as responding variable) is the heat of combustion. We measure the released energy by its ability to warm up some water. One calorie is the amount of energy that can increase the temperature of 1 ml of water by 1 degree Celsius.
Controlled variable is the room temperature. Perform all experiments at the same time or in the same room temperature.
Constants are the experiment method, amount of water, size of water container and all other experiment procedures, instruments and conditions.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
It is difficult to have a calculated guess or hypothesis in this case. The energy released by burning a fuel, is the same energy that keeps the atoms of that fuel together. By burning we brake the bonds between carbon-carbon and carbon-hydrogen in the fuel molecules. Some fuels have more carbon-hydrogen bonds than others. If breaking the bond between carbon and hydrogen creates more energy, Methane (CH4) must be the most efficient fuel. Other factors may be involved that we didn’t think about. For example in some fuels part of the energy produced by burning may be consumed by the same fuel, for example, to melt it or evaporate it. So in this case we directly go to do the experiment to see what the result are.
Now you are playing with fire. It is dangerous and can be fatal. If you are a beginner, do it while supervised by a fire safety trained adult. Also do it in a safe place. My favorite place for such experiments is a large concrete room with enough safety equipment and a fire extinguisher. My second choice is an open area away from vegetation, woods, buildings or anything else that may catch on fire. Always do fire and chemical experiments as small as possible and keep your experiment area away from your supply area. Wear safety glasses and protecting clothing.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
In order to find the heat of combustion, you will first use the energy from burning a fuel to heat a known quantity of water. By monitoring the temperature of the water, you can find the amount of heat transferred to it, using the formula
where q is heat, m is the mass of water, and Dt is the change in temperature of the water. Finally, the amount of fuel burned will be taken into account by calculating the heat per gram of fuel consumed in the combustion.
1. Obtain and wear goggles.
2. Prepare your heating apparatus, scale, thermometer, water and fuel sample. To learn more about heating apparatus see the end of this page.
Part 1 Paraffin Wax
3. Prepare a candle for the experiment by holding a lighted match near its base, so that some melted wax falls onto a 3″ X 5″ index card. Immediately push the candle into the melted wax and hold it there for a moment to fasten it to the card.
4.Find and record the combined mass of the candle and index card (or the alcohol burner and contents in Part 2 below).
5. Determine and record the mass of an empty can. Add 100 mL of chilled water to the can (use 200 mL of chilled water in Part 2). Determine and record the mass of the can and water.
6. Set up the apparatus as shown in the picture. Use a ring and stirring rod to suspend the can about 5 cm above the wick. Use a utility clamp and slit stopper to suspend the thermometer in the water. The thermometer should not touch the bottom of the can. Important: The thermometer must be in the water for a least 45 seconds before you do Step 7.
7. Record the time, light the candle (or alcohol burner in Part 2). Record the initial temperature. Heat the water until its temperature reaches 40°C and then extinguish the flame. CAUTION: Keep hair and clothing away from an open flame.
8. Continue stirring the water until the temperature stops rising. Record this final temperature.
9. Determine and record the final mass of the cooled candle and index card, including all drippings (or the cooled alcohol burner and contents in Part 2).
10. Now you can record your data and start necessary calculations. See the calculations section (below) for a sample of data table and step by step calculations instructions.
Part 2 Ethanol
11. Repeat Steps 4-10 using ethanol in an alcohol burner. Be sure to use 200 mL of chilled water in Step 5.
Why do we use more water while testing Ethanol?
The reason is that alcohol has a higher combustion heat than paraffin wax. (we know it from gathered information or previous experiments).
By using double amount of water in testing alcohol, we ensure that the starting water temperature and the ending water temperature are almost the same in our two experiment. This is important because cold water gets more heat from the environment, but as it gets hot the rate of heat transfer will reduce. That is why we stop heating when the water temperature gets to 40°C.
Information are available at:
Just to make sure that the temperature increase in water is only caused by the burning fuel (not an unknown factor), you will need a control experiment.
Control experiment is another container of water (identical to the one you used in your experiment). Place it away from your experiment and measure its water temperature before and after your main experiment.
If the temperature in the control experiment is not changes, you have to do nothing else.
If the temperature in the control experiment is increased (for example 2 degrees), then you must deduct the same amount from the temperature increase in your main experiment.
For example in your main experiment you may have a temperature increase of 37 degrees. You deduct 2 and the actual temperature increase caused by fuel will be 35.
Note: Temperature increase in the control experiment may be caused by temperature increase in the room.
Materials and Equipment:
100-mL graduated cylinder
alcohol burner with ethanol
3″ X 5″ index card
Results of Experiment (Observation):
PROCESSING THE DATA
1. Find the mass of water heated.
2. Find the change in temperature of the water, Dt.
3. Calculate the heat absorbed by the water, q, using the formula in the introduction of this experiment.
4. Find the mass of paraffin or ethanol burned.
5. Calculate the heat of combustion for paraffin and ethanol, in calories. Use your Step 3 and Step 4 answers.
6. Calculate the % efficiency in both trials of the experiment.
How do I do that?
Divide your experimental value (in kJ/g) by the accepted value, and multiply the answer by 100. The accepted heat of combustion of paraffin is 9,919 calories/g (or 41.5 kJ/g), and for ethanol the value is 7,170 calories/g (or 30.0 kJ/g).
1 calorie is the amount of energy required to raise the temperature of 1 g of water by 1 °C.
1 calorie = 4.184 J
7.Based on your results, which fuel produces more energy per gram burned? Give an explanation for the difference. (Hint: Ethanol, C2H5OH, is an oxygenated molecule; paraffin, C25H52, does not contain oxygen.)
8. Suggest some advantages of using ethanol (or paraffin) as a fuel.
9. Discuss heat loss factors that contribute to the inefficiency of the experiment.
You can repeat this procedure with natural gas (which is a combination of Methane and Ethane), Canned or liquid gas (which is Propane and/ or Butane), Gasoline (Very dangerous), Wood, Charcoal, and heating oil, vegetable oil.
SAMPLE DATA TABLE AND CALCULATIONS
Rows with green background are calculated.
|Initial mass of fuel + container||
|Final mass of fuel + container||
|Mass of fuel burned||
|Mass of can and water||
|Mass of empty can||
|Mass of water heated||
|Final temperature, t2||
|Initial temperature, t1||
|Temperature change, Dt||
|Energy in calories|
|Energy in kJ (Kilo Joules)|
|Heat of combustion kJ/g (Experimental)|
|Known or accepted heat of combustion||41.5 kj/g||30.0 kj/g|
- To calculate the mass of fuel burned, deduct the final mass of fuel from the initial mass of fuel.
- To calculate the mass of water heated, deduct the mass of can from the mass of can with water.
- To calculate the temperature change, deduct the initial temperature from the final temperature
- To calculate energy in calories, multiply the temperature change by the mass of water.
- To convert energy from calories to kilo joules, first multiply the energy in calories by 4.184 to convert it to joules, then divide the result by 1000 to make it kJ (Kilo Joules)
- To calculate the heat of combustion, Divide the energy in kJ by the mass of fuel burned.
- To calculate efficiency, divide your experimental heat of combustion by the known heat of combustion.
If the efficiency is 60%, it means that 40% of the energy is wasted or lost in different forms and only 60% of the energy is used to heat up water.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
I found a nice program that calculates the heat of combustion for pure or mixture of gases. URL to this program is: http://www.processassociates.com/process/property/hc_gas.htm
You enter percentage of each possible ingredient and select the units, it does the rest.
You have many choices on how to assemble a heating apparatus. It also depends on the material and equipment that you will have access to.
As a water container you can use a Pyrex glass beaker or erlen meyer flask or you may use a metal container such as steel cup or aluminum cup. You may even use an empty soda can as your water container. The opening is large enough for a thermometer to enter, so you will not need to do any changes on that.
The thermometer is better to be a glass thermometer used in laboratories, but if you don’t have one, use a room thermometer or food thermometer. These are not as accurate as laboratory glass thermometers, but they do the job. However, you cannot use a medical, mercury thermometers.
Somehow you need to keep your water container elevated so you can slide the burner under it. You can build a stand or hang it from somewhere. Use your creativity.
As you see in this picture, the water container and burner have no insulation. So, part of the heat will be wasted.
It is good to somehow cover your setup with heat insulators. To start, you can use a larger metal can that may also serve as a stand. Place it up-side down, cut an opening on the side to slide in the heat source. Also make another opening on the top to hold your water container. To make it more efficient, you may cover it with sheets of nonflammable insulating material.
Instead of a larger metal can, you can just use rigid insulating material and assemble it to prevent any waste of heat in your apparatus.
Alcohol burner can be used for many liquid fuels. To test gasses such as propane, use small propane containers and burners available from hardware stores.
To test wood, use wood chips produced while planning the wood. Those chips are very thin and burn easily while dry.