Students who demonstrate understanding can: Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes.*
Clarification statement: Emphasis is on the design, controlling the transfer of energy to the environment, and modification of a device using factors such as type and concentration of a substance. Examples of designs could involve chemical reactions such as dissolving ammonium chloride or calcium chloride.
Assessment boundary: Assessment is limited to the criteria of amount, time, and temperature of substance in testing the device.
Official wording from the Next Generation Science Standards (NGSS Lead States, 2013). NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the NGSS were involved in the production of this page, and they do not endorse it. View on nextgenscience.org
Some chemical processes give off thermal energy to their surroundings and feel warm; others take thermal energy in and feel cold. Dissolving calcium chloride in water warms the water, while dissolving ammonium chloride cools it. Instant hot packs and cold packs used for sports injuries rely on exactly these processes.
Here students act as engineers. They define what the device must do, for example reach at least 10 degrees Celsius above room temperature and stay warm for 5 minutes, then build a prototype, test it, and change one factor at a time. Useful factors include which substance is used, how much of it, how much water, and how well the container is insulated. Each round of testing gives data that drives the next improvement.
The scope is deliberately narrow: performance is judged by amount of substance, time and temperature. Students do not need to calculate the total thermal energy transferred. What matters is a fair test, honest data and a design choice they can justify.
Students often think the pack sends cold into an injury. In fact the process absorbs thermal energy from its surroundings, including your skin, which is why it feels cold.
Adding more solid may raise the peak temperature, but it can also cost more, waste material or exceed what can dissolve. Good designs balance several criteria.
A single trial can be off because of a slip in measuring. Engineers repeat tests and change only one variable at a time so they know what caused each improvement.
Many students only know fire and expect all chemical changes to release heat. Show an endothermic dissolving process where the thermometer drops.
A team's hand warmer uses 10 g of calcium chloride in 50 mL of water. It rises from 21 to 29 degrees Celsius but the goal is at least 33 degrees Celsius. In a second test with 20 g in the same 50 mL, it reaches 36 degrees Celsius. What should the team conclude and do next?
Answer: Doubling the calcium chloride raised the temperature change from 8 to 15 degrees Celsius and met the goal; the team should repeat the trial and then work on how long the device stays warm.
Run the project in short cycles: plan, build, test, improve. A shared class data table lets groups compare substances and amounts, and a simple temperature versus time graph makes the comparison obvious. Insist on goggles and on small, measured amounts.
This performance expectation pairs naturally with MS-ETS1-1 (defining criteria and constraints) and MS-ETS1-3 (comparing test data across designs), so assessment may ask students to pick the best design from a table or suggest the next change to test.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: A) The process absorbs thermal energy from the surroundings
A falling temperature means the process is taking thermal energy from the water and container, so it would work as a cold pack.
Answer: D) The volume of water and the type of solid
In a fair test only the mass of solid changes. Water volume, type of solid, container and starting temperature should all stay the same.
Answer: 12 (also accepted: 12 degrees)
The temperature change is 32 - 20 = 12 degrees Celsius.
Answer: B) It absorbs thermal energy from the skin
The chemical process inside takes in thermal energy from whatever touches it, including your skin.
Answer: A) It must cost less than one dollar to make
Criteria describe what the device must achieve. Constraints are limits on the design, such as cost, materials or safety.
Answer: exothermic
Exothermic processes release thermal energy, so their surroundings warm up.
Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
A full lesson with slides, activities and an exit ticket on designing a hot or cold pack, pitched to grades 6-8 and editable in PowerPoint or Google Slides.
Make a lesson βA printable, differentiated worksheet on MS-PS1-6 with an answer key, ready in about a minute.
Make a worksheet βTurn designing a hot or cold pack into a quiz students answer online that marks itself, with a class summary for you.
Build a test βNo. Assessment is limited to the amount of substance, time and temperature. Students compare measured temperature changes rather than calculating joules.
Common classroom choices are calcium chloride, which warms water as it dissolves, and ammonium chloride, which cools it. Always use measured small amounts and eye protection.