Bring on the Heat! Investigating Exothermic Reaction Rates
AbstractHave you ever pulled a muscle or just been sore after a long day of work or exercise? Hot showers are great, but maybe you've used the more convenient heat packs. Heat packs, which you can buy at grocery or drug stores to soothe aching muscles, use exothermic reactions to produce a low level of heat that lasts for an extended period of time. Exothermic reactions change chemical energy into heat energy. In this chemistry science fair project, you will use heat packs to study the heat-generating reaction of oxygen with the iron within them.
The objective of this chemistry science fair project is to investigate how changing the level of oxygen affects the exothermic oxidation of iron powder.
David Whyte, PhD, Science Buddies
Cite This PageGeneral citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.
Last edit date: 2017-07-28
Heat packs are available in most grocery and drug stores to provide "fast-acting pain relief." When the package surrounding the heat pack is opened, the heat pack slowly warms up, and stays warm for up to 12 hours. But how do they work? The production of heat requires an energy source. The energy that heats up the pack is generated by the reaction of iron in the heat pack with oxygen in the atmosphere. The pack stays at room temperature as long as it is protected from air. When the package is opened, oxygen (O2) is free to combine with the iron (Fe) in the pack to form iron oxide (Fe2O3), as shown in the chemical equation below:
|4 Fe (s) + 3 O2 (g) → 2 Fe2O3 (s) + heat energy|
This is the same process by which iron is turned to rust, but in the heat pack, it occurs fast enough for the heat to be noticeable. Reactions that produce heat are referred to as exothermic.
The ingredients of most heat packs include iron powder, water, activated charcoal, vermiculite, and salt. The iron powder is the "active ingredient" that fuels the reaction. What are the other ingredients for? They promote the reaction and help to distribute the heat. In particular, the salt acts as a catalyst, the carbon helps disperse the heat, the vermiculite is used as an insulator for the purpose of retaining the heat, and water is required for the reaction. All of these ingredients are surrounded by a polypropylene bag that lets air in, but contains the moisture.
The reaction proceeds at a rate that is determined, in part, by the concentration of oxygen. In chemistry, the law of mass action states that the rate of a reaction is proportional to the product of the concentrations of the participating molecules. Thus, if the concentration of oxygen is increased, the rate of the reaction will also increase. As the reaction rate increases, so does the amount of heat produced. The Experimental Procedure of this science fair project presents two methods for varying the level of oxygen available to drive the reaction. To increase the concentration of oxygen, pure oxygen gas from a pressurized canister is gently blown over a heat pack. To decrease the concentration of oxygen, clear tape is used to cover either 50 percent or 75 percent of the air-permeable surface. You will use an infrared thermometer to measure the temperature of the heat pack. The infrared thermometer allows you to take the temperature of the heat pack just by pointing the thermometer at the hot surface.
Terms and Concepts
- Chemical equation
- Exothermic reaction
- Law of mass action
- The chemical equation above is a simplified version of the overall process involved in the oxidation of iron. Look up the details in a chemistry textbook or online. What is the role of water in the reaction? What is the oxidation state of iron in the product?
- How does the chemistry that describes iron rust compare to the chemistry of wood combustion?
- Wikipedia Contributors. (2008, October 21). Rust. Wikipedia: The Free Encyclopedia. Retrieved October 20, 2008, from http://en.wikipedia.org/w/index.php?title=Rust&oldid=246762027
News Feed on This Topic
Materials and Equipment
- Oxygen canister, with regulator and hose. This can be purchased as part of a torch kit from most hardware stores. For example, the Benzomatic torch OX2550KC Cutting, Welding and Brazing Torch Kit (OX2550KC) has an oxygen canister with a regulator and hose. You will not be using the propane part of the torch, just the oxygen part.
- Heat packs (15), must contain iron powder
- Masking tape
- Permanent marker
- Ceramic bowls, matching (5)
- Infrared (IR) thermometer; available online from retailers such as Amazon.com
- Clear tape
- Lab notebook
- An adult helper
Disclaimer: Science Buddies occasionally provides information (such as part numbers, supplier names, and supplier weblinks) to assist our users in locating specialty items for individual projects. The information is provided solely as a convenience to our users. We do our best to make sure that part numbers and descriptions are accurate when first listed. However, since part numbers do change as items are obsoleted or improved, please send us an email if you run across any parts that are no longer available. We also do our best to make sure that any listed supplier provides prompt, courteous service. Science Buddies does participate in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity. If you have any comments (positive or negative) related to purchases you've made for science fair projects from recommendations on our site, please let us know. Write to us at firstname.lastname@example.org.
Remember Your Display Board Supplies
Poster Making Kit
ArtSkills Trifold with Header
The goal of this experiment is to demonstrate that increasing the amount of oxygen available to react with the iron will increase the amount of heat produced by the exothermic reaction. There are two ways you will vary the oxygen for this experiment:
- Use the oxygen in the oxygen canister to increase the reaction rate.
- Use the clear tape to cover up a portion of the air-permeable surface of the heat pack, thus decreasing the rate of the reaction.
Note: The reaction starts as soon as the wrapper is removed from the heat pack, so you should record the time at which you open each pack. Work as efficiently as possible, but because the reaction proceeds relatively slowly (it takes about a minutes to feel the heat after the pack is opened), you do not need to rush.
Preparing the Initial Setup
Assemble the oxygen canister and regulator.
- Screw the oxygen canister into the regulator. Note that the oxygen tank may have a reverse thread. Turn the knob to check that oxygen flows. Close the oxygen valve.
- Place a heat pack next to each of the five ceramic bowls.
Using the masking tape and permanent marker, label the bowls and the heat packs 1 to 5:
- #1: 100% surface area open, air, no pure oxygen
- #2: 100% surface area open, pure oxygen
- #3: 50% surface area open, air, no pure oxygen
- #4: 25% surface area open, air, no pure oxygen
- #5: Unopened package
- Use the IR thermometer to measure the temperature of the unopened heat packs.
- Make three data tables for each heat pack, since you will need one table for each of the three trials.
- Record the time and temperature for each unopened heat pack.
Preparing the Heat Packs
In the procedure below, you will be recording the temperature of all five packs every few minutes.
- Open the wrapper for heat pack #1 and place it in bowl #1, with the air-permeable side facing up.
- Start the stopwatch. Use the time on the stopwatch for all of your readings, from the time you start until the experiment is complete. Restart the stopwatch for each new trial (not every time a new heat pack is opened) —there will be three trials. You can have your helper record the data as you take the temperatures.
- Record the time the wrapper was taken off.
- Open the wrapper for heat pack #2 and place it in bowl #2. Record the time.
- Open the wrapper for heat pack #3, and cover 50% of the perforated surface with clear tape. Place it in bowl #3. Record the time.
- Open the wrapper for heat pack #4, and cover 75% of its perforated surface with clear tape. Place it in bowl #4. Record the time.
- Place an unopened heat pack in bowl #5. This is a control to track room temperature.
- Make sure all of the heat packs have the air-permeable side facing up.
- Record the temperature of each of the heat packs every 2 minutes or so for the first 10 minutes.
Adding the Oxygen
In the next step, oxygen from the canister will be used to accelerate the reaction in heat pack #2. Record the temperature of heat pack #2 before and after each oxygen treatment. You will then record the temperature of all heat packs every 5 minutes.
- Open the valve on the oxygen canister until you have a gentle stream of oxygen.
- Gently blow the oxygen over the surface of heat pack #2 for 60 seconds. You can use the stopwatch that should still be running to see when 60 seconds have passed. Do not stop the stopwatch to do this.
- Take the temperature of all of the heat packs.
- Repeat steps 1-3 of this section every 5 minutes, for a total time of 90 minutes. Record all data in your lab notebook.
- Repeat the entire experiment two more times with new heat packs and average the results. Record the averages in your lab notebook.
Analyzing Your Results
Graph your data: time in minutes on the x-axis and temperature on the y-axis.
- For precise time measurements, convert time from minutes and seconds to decimal minutes.
- Temperature for heat pack #2 may be "bumpy."
- How long did it take for each sample to reach a steady temperature? How did changing the surface area of the perforated region affect the rate of heating? Which pack had the highest temperature?
Communicating Your Results: Start Planning Your Display BoardCreate an award-winning display board with tips and design ideas from the experts at ArtSkills.
If you like this project, you might enjoy exploring these related careers:
ChemistEverything in the environment, whether naturally occurring or of human design, is composed of chemicals. Chemists search for and use new knowledge about chemicals to develop new processes or products. Read more
Chemistry TeacherWhen you hear the word chemicals, you might think of laboratories and scientists in white coats; but actually, chemicals are all around you, as well as inside of you. Everything in the world is made up of chemicals, also known as matter, or stuff that takes up space. Chemistry is the study of matter—what it is made of, how it behaves, its structure and properties, and how it changes during chemical reactions. Chemistry teachers are the people who help students understand this physical world, from the reactions within our own bodies to how soaps and detergents work and why egg proteins can keep a cookie from crumbling. They prepare the next generation of scientists and engineers, including all healthcare professionals. They also help also students develop scientific literacy. Read more
Chemical TechnicianThe role that the chemical technician plays is the backbone of every chemical, semiconductor, and pharmaceutical manufacturing operation. Chemical technicians conduct experiments, record data, and help to implement new processes and procedures in the laboratory. If you enjoy hands-on work, then you might be interested in the career of a chemical technician. Read more
WelderWhat do race cars, bridges, boats, computers, bikes, and cell phones all have in common? They all require welding, or using tools to permanently bond pieces of metal together. Welders' skills are needed to assemble many of the objects you encounter and use every day. A career in welding could take you to the garage for a famous car race, to the tops of the highest buildings, or even to the bottom of the ocean! Read more
- Use continuous oxygen exposure for heat pack #2. However, be careful not to let the pack get too hot.
- Calculate the rate of temperature change for each sample. At what point after opening the package is the rate the highest?
- Place a heat pack into a plastic baggie after it has heated up. Record its temperature at various times and graph the results.
- Catalase is an enzyme that produces oxygen when exposed to hydrogen peroxide. Devise experiments in which you use heat packs to monitor oxygen produced by catalase (potatoes and chicken livers are two sources for the catalase enzyme).
- How does exposure to pure oxygen affect the overall "life" of the heat pack?
Ask an ExpertThe Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.
Ask an Expert
News Feed on This Topic
Looking for more science fun?
Try one of our science activities for quick, anytime science explorations. The perfect thing to liven up a rainy day, school vacation, or moment of boredom.Find an Activity