How to Measure Thermal Energy Released from a Flame

Co-authored by Bess Ruff, MA

Last Updated: October 8, 2020

When something burns, it releases energy in the form of heat and light. The amount of energy released by a particular flame differs depending on the fuel that is being burnt. You can test the amount of energy released by a fuel by measuring the temperature change that the flame creates in a container of water. One of the ways to measure the energy is by constructing a calorimeter, which measures the amount of heat involved in a chemical reaction or thermal process.

Part 1

Part 1 of 3:

Building a Simple Calorimeter

It is important to know exactly how much water you are using. This will allow you to calculate how much energy was used to heat the water. Use a graduated cylinder to accurately measure 100 milliliters (3.4 fl oz) of water for the experiment. Record this amount in a notebook.^{[1]
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An aluminum soda can will conduct heat more efficiently than a glass cylinder. Be careful not to spill any of the water. It is important that the amount of water you recorded is correct.^{[2]
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3
Set the can over your fuel source. Since heat rises, you will get the most heat transfer if the can is placed directly over the fuel source. Use a stand or build a simple apparatus of some kind to hold the can 6–8 centimetres (2.4–3.1 in) above the fuel source. Use metal to hold the can in place.^{[3]
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- Materials like wood or plastic might melt or catch fire, so be sure to use fire-safe materials to construct the stand.
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Part 2

Part 2 of 3:

Measuring Temperature Changes

1
Measure the initial temperature of the water. Without the initial temperature of the water, you will be unable to know how much heat was absorbed. Put a thermometer into the water and take a reading. Write down the reading so that your remember it exactly.
- For example, your initial reading might be 20 °C (68 °F). It is best to take the measurement in Celsius, as this will simplify your math later on.
2
Ignite the fuel under the water. Use a match or grill lighter to ignite the fuel. Common fuels to test include peanut oil, vegetable oil, methanol, or ethanol. This step should be done by or with a supervising adult.^{[4]
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- Wear gloves and goggles to protect your eyes and hands.
- Before you ignite the fuel, devise a safety plan in case anything goes wrong or the fire spreads. Keep a fire extinguisher nearby.
3
Take a final temperature reading of the water. After all of the fuel has burned, or you extinguish it, you will need a second temperature reading. Use the same thermometer and insert it into the water. Record the final temperature for use in calculating the energy released by burning the fuel.
- Your final reading should be higher than your initial reading. For example, it might be around 24 °C (75 °F), depending on your fuel.
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Part 3

Part 3 of 3:

Calculating Energy Released

1
Find the difference in temperature. Subtract the initial temperature from the final temperature. This will tell you how much the water temperature was changed by the burning fuel underneath. Convert this number to Celsius if you your measurements were not in Celsius.
- You can convert a number from Fahrenheit to Celsius by using the equation $C=(F-32)x5/9$ where C is the temperature in Celsius and F is the temperature in Fahrenheit.
- An example is 24 °C (75.2 °F) - 20 °C (68.0 °F) = 4 °C (39.2 °F).
2
Multiply the temperature difference by the specific heat of water. The specific heat of water is the amount of heat it takes to raise the temperature of 1 gram of water by 1 degree Celsius. For water, the specific heat is 1 calorie per gram Celsius. That means it takes 1 calorie to heat 1 gram of water by 1 degree Celsius.^{[5]
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- The unit for specific heat is written as 1 calorie / (gram x degrees Celsius).
- Multiplying this by the temperature difference yields 4 degrees Celsius x 1 calorie / (gram x degree Celsius) = 4 calories / gram.
3
Factor in the mass of the water. Now, multiply the product of the heat difference and specific heat by the amount of water you used. Note that 1 mL of water is equal to 1 gram of water. Make sure you are using the unit grams.^{[6]
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- This will yield your energetic release: 4 calories / gram x 100 grams = 400 calories.
4
Realize that your system loses some energy. While some of the heat released is going directly up and into the water, your system is not perfect. Some heat will be lost to the surrounding air. A small amount of heat will also be absorbed by the can itself. There is little that can be done to compensate for the heat loss.^{[7]
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- If you are trying to do highly precise experiments, you may invest in a commercial calorimeter, but even then the results may not be 100% efficient.
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Tips

Secure the can carefully to a stand to make sure it does not tip over or fall on the flame. Also, ensure that the can is not near the laptop. Also, make sure that the can is not touching the flame. There should be some space between it.

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Warnings

The fumes from some substances are toxic. If you don't have a fume hood that you know how to use, stick to household fuels like candles.

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Fire is extremely dangerous and you can be burned easily. Be careful with it and always keep a fire extinguisher handy.

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