Chapter 14 · Unit 5: Chemical Reactions · Segment 2

Energy in Chemical Reactions

How does energy move between a chemical reaction and its surroundings, and how can engineers control that flow to build a useful device?

MS-PS1-6 · assessesMS-ETS1-3 · assessesMS-ETS1-4 · practiceMS-ETS1-2 · assessesMS-ETS1-1 · assesses Textbook pp. 172–181 1 presentation · 10 worksheets · 3 labs
Student bundle (no keys) (9.3 MB)Teacher bundle (password) (13.4 MB)

Overview

Students figure out that every chemical reaction moves energy across a boundary between the reacting matter (the system) and everything around it (the surroundings), and that the direction of the net flow is what makes a reaction exothermic or endothermic. They learn to read that direction from evidence (warming, cooling, light, sound), to explain it qualitatively with bond breaking and bond forming, and to show it in a chemical equation. The second half of the chapter is engineering: students design, test and improve a pack that warms or cools using safe reagents, judging each prototype by amount, time and temperature exactly as hand-warmer engineers do. The chapter builds on the atom-regrouping ideas of Lesson 13 and sets up the chemical-engineering decisions of Lesson 15.

Estimated class time: presentation about 120 minutes · worksheets about 380 minutes in total · labs 4 sessions. Seven 50-minute periods: two for the phenomenon, system and surroundings, and the exothermic/endothermic distinction with the mystery-packet lab; one for bonds, conservation and energy in equations; three for the engineering strand (prototype story, design-challenge lab across two sessions, data-decision lab); one for synthesis and mastery.

Phenomenon

Two white pouches, one squeeze, opposite results

A camping-store clerk sets two identical-looking white pouches on the counter. Each holds a dry powder and a small inner bubble of water. She squeezes the first pouch until the bubble bursts and hands it over: within a minute it is almost too warm to hold, and a thermometer pressed against it reads about 45 °C. She squeezes the second one the same way: it turns cold enough to fog with condensation, and the thermometer reads about 5 °C. (These readings are illustrative values, typical for instant hot and cold packs.) Nothing was plugged in, lit, or chilled. The same action warmed one pouch and chilled the other. Where did the energy come from in the first pouch, and where did it go in the second?

Notice and wonder prompts

  • What exactly changed inside each pouch when the water bubble burst?
  • The warm pouch gives energy to your hand. Does the cold pouch give 'cold' to your hand, or does something flow the other way?
  • Why does each pouch eventually return to room temperature, and could you make it last longer?
  • If you doubled the powder in a pouch, would it get twice as hot, or stay hot twice as long, or both?

Learning targets

  • I can identify the system and the surroundings in a chemical reaction and use evidence (warming, cooling, light, sound) to decide which way energy flows.
  • I can explain qualitatively why a reaction is exothermic or endothermic by comparing the energy needed to break bonds with the energy released when new bonds form.
  • I can show the direction of energy flow in a chemical equation by writing energy with the reactants or with the products.
  • I can design, test and modify a device that releases or absorbs thermal energy, using criteria of amount, time and temperature to decide what to change next.
  • I can analyze test data from several prototypes to find the characteristics that worked best and combine them into an improved design.

What shows the learning happened

  • A completed Lab 1 recording sheet that classifies four mystery packets as exothermic, endothermic or neither from measured temperature changes, with the system and surroundings labeled for stations A and B.
  • A Lab 2 design record showing three prototypes, the single change made each time, the temperature-versus-time data for each, and a written justification of the final design against every criterion and constraint.
  • A Lab 3 decision table that matches prototypes to users, a graph of three prototypes' temperature curves, and a written proposal for a new design that combines the best characteristics with a predicted result.
  • A Claim-Evidence-Reasoning paragraph (W6) that uses temperature data to argue whether a change is exothermic or endothermic and explains the direction of energy flow using bonds.
  • A correctly completed equation task (W4, W10) that places the energy term with the reactants or the products and explains why the word energy does not change the atom count.
  • An exit ticket that distinguishes a design criterion from a constraint and names the direction of energy flow in a cold pack.

Key vocabulary 12 terms

systemThe matter you are following in a reaction: the reactants and the products they become, inside an imaginary boundary you draw so you can track energy crossing it.For a burning candle, the system is the wax and the oxygen that react plus the carbon dioxide and water vapor they turn into.
surroundingsEverything outside the system that can exchange energy with it, such as the container, nearby air, water in a beaker, or the hand holding a pack.When the surroundings of a reaction get warmer, energy must have crossed the boundary out of the system.
exothermic reactionA reaction in which the system gives out more energy than it takes in, so the net flow of energy is out to the surroundings. The energy can leave as heat, light or sound.Burning magnesium is strongly exothermic: the surroundings receive a blast of thermal energy and a flash of white light.
endothermic reactionA reaction in which the system takes in more energy than it gives out, so the net flow of energy is in from the surroundings, which usually cool down. The word also describes other changes that absorb energy, such as some salts dissolving.Mixing citric acid and baking soda in water is endothermic, so the cup feels cold a few seconds after the fizzing starts.
thermal energyThe energy a sample of matter has because its particles are moving. When thermal energy moves from a warmer object to a cooler one, that transfer is called heat.A hand warmer works by transferring thermal energy from the reacting iron to your skin.
temperatureA measure of how fast the particles in a sample are moving on average, read with a thermometer or probe. It is not the same as the amount of thermal energy, which also depends on how much matter there is.Two prototypes reached the same temperature, but the heavier one stayed warm longer because it held more thermal energy.
chemical bondAn attraction that holds atoms together in a molecule or an extended structure. Pulling bonded atoms apart always takes energy in; forming a new bond always gives energy out.A reaction is exothermic when the energy given out by forming new bonds is greater than the energy needed to break the old ones.
net energy transferThe overall direction and size of the energy flow between a system and its surroundings after adding up everything absorbed and everything released.A match needs a small energy input to start, but its net energy transfer is outward, so burning is exothermic.
prototypeA working version of a design that is built so it can be tested, with the results used to decide what to change in the next version.The team's first prototype reached only 30 °C, so they doubled the reagent in the second prototype.
criteriaThe measurable goals a design must meet to count as a success, such as a target temperature or a minimum working time.One criterion for the cold pack was that it drop at least 8 °C below the starting temperature within two minutes.
constraintsThe limits a design must stay within, such as a budget, a safety ceiling, a maximum mass or the materials available.A hand warmer that reaches 60 °C would burn skin, so a maximum of 50 °C is a constraint, not a criterion.
iterationOne round of the build-test-modify cycle. Engineers repeat iterations, using the data from each round to choose the next change.By the third iteration the pack met the time criterion but still cost more than the budget allowed.

Standards alignment

California NGSS, Grade 7 Preferred Integrated Course Model. Each entry says whether this chapter's work assesses the performance expectation, gives practice toward it, or supports it as background; the resource lists below repeat this for every worksheet and lab.

MS-PS1-6Assesses: the whole PE: construct, test and modify a device that releases or absorbs thermal energy by chemical processesCA Grade 7

Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes.

Lab 2 has students build a warming or cooling pack from teacher-measured safe reagents, test it against criteria of amount, time and temperature, and modify it twice across three prototypes, which is the evidence the PE asks for and stays inside its assessment boundary. W9 is the paper version of the same design task. The clarification statement names dissolving calcium chloride and ammonium chloride as acceptable chemical processes, so the calcium chloride hot pack qualifies even though dissolving is not a reaction in the strict sense.

Assessment boundary: Assessment is limited to the criteria of amount, time, and temperature of substance in testing the device.

MS-ETS1-3Assesses: analyzing test data from several solutions to combine the best characteristics into a new oneCA Grade 6-8

Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.

Lab 3 gives students test data from six simulated hand-warmer prototypes, asks what each did well and badly for three different users, and requires them to propose a new design that combines the best characteristics. W5 practices the same data analysis on a smaller set.

MS-ETS1-4Practice toward: iterative testing and modification of a physical prototypeCA Grade 6-8

Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

In Lab 2 the prototype pack is the model that generates temperature-over-time data, and students use that data to modify the next version. The lesson text models this cycle with the hand-warmer engineers. Students do not develop their own model from scratch, so this is practice toward the PE rather than full evidence of it.

MS-ETS1-2Assesses: evaluating competing designs systematically against criteria and constraintsCA Grade 6-8

Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

W9 produces evidence for it: students evaluate four cold-pack designs in a pass-or-fail decision table against criteria and constraints they wrote themselves from a user's letter. Lab 3, W8 and the slide-21 task practice the same systematic process with supplied criteria.

MS-ETS1-1Assesses: defining criteria and constraints precisely, including limits that protect people and the environmentCA Grade 6-8

Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

W9 has students turn a school nurse's letter into six precise criteria and constraints, computing the per-pack cost limit and naming the rules that protect runners and the playing field. Lab 2 supports it by having teams restate a supplied brief in their own words and say how each item will be tested.

Science and engineering practices

  • Constructing Explanations and Designing Solutions. Students explain the direction of energy flow in four mystery packets (Lab 1) and in a hand-warmer test (W6) and design, test and modify a warming or cooling pack that meets stated criteria (Lab 2, W9).
  • Analyzing and Interpreting Data. Students graph temperature against time for their own packs and for simulated prototypes, find the peak, the time above a threshold and the rate of warming or cooling, and use those values to choose the next modification (Lab 2, Lab 3, W5).
  • Developing and Using Models. Students use a system-and-surroundings boundary model, a bond-breaking and bond-forming energy model, and energy-in-the-equation notation to represent reactions they cannot see (W4, presentation slides 6, 13 and 16).

Disciplinary core ideas

  • PS1.B Chemical Reactions. Some reactions release energy to the surroundings and others absorb energy from them (the DCI's 'store energy'); the energy change comes from the difference between breaking old bonds and forming new ones, and it can be tracked as a flow between system and surroundings.
  • ETS1.B Developing Possible Solutions. A prototype has to be tested and then changed according to what the tests showed; students do this three times in Lab 2 and read the hand-warmer engineers doing it in the lesson.
  • ETS1.C Optimizing the Design Solution. No single prototype wins every test; students identify which characteristic performed best in each test and combine them (Lab 3), then iterate toward a design that meets all the criteria (Lab 2).

Crosscutting concepts

  • Energy and Matter. Energy is tracked crossing the boundary of a system; it is transferred and stored, never created or destroyed, so a release in one place means a loss somewhere else.
  • Systems and System Models. Students draw the boundary that separates the reacting matter from its surroundings and use it to decide what counts as 'in' and 'out' for every example in the chapter.
  • Cause and Effect. Changing one factor at a time (amount of reagent, volume of water, insulation, how fast air reaches the iron) lets students link a specific cause to a specific change in temperature or time.

Presentation 26 slides

Energy in Chemical Reactions: tracking the flow and building a device that uses it. Original, editable slides with speaker notes: a phenomenon opener, learning targets, the chapter's concepts with diagrams, vocabulary in context, 4 checks for understanding, 2 discussion prompts, an application task, a misconception check, a synthesis and an exit ticket.

PowerPoint (editable)Slides PDFSpeaker notes PDFSpeaker notes (web)

Worksheets 10 of 10

Ten different tasks, one per instructional blueprint. Each has a student PDF (low ink, US Letter), an editable DOCX, an HTML preview, and a separate teacher answer key with reasoning.

First page of Keeping the Books on Energy: Where It Goes When Matter Changes
Worksheet 3 · Reading with evidence

Keeping the Books on Energy: Where It Goes When Matter Changes

I can use evidence from a passage to explain how energy crosses the boundary between a reaction and its surroundings, why it never simply appears, and how engineers use that flow in a device.

35 minindividualBuilds understandingReadingWriting MS-PS1-6 · supports
Student PDFStudent DOCXPreview
Teacher only
Answer key PDFAnswer key DOCXKey preview
First page of Three Prototypes, One Winter: Reading Hand-Warmer Test Curves
Worksheet 5 · Data and graphing

Three Prototypes, One Winter: Reading Hand-Warmer Test Curves

I can graph temperature-versus-time data from three hand-warmer prototypes, calculate peak rise, warming rate and time above a threshold, and decide which prototype meets the criteria and which characteristics to combine.

45 minindividualPracticeData analysisIndependent practice MS-ETS1-3 · practiceMS-PS1-6 · practice
Student PDFStudent DOCXPreview
Teacher only
Answer key PDFAnswer key DOCXKey preview
First page of Which Way Did the Energy Go? An Evidence Sort for Pack Designers
Worksheet 8 · Collaborative investigation

Which Way Did the Energy Go? An Evidence Sort for Pack Designers

I can work with a group to sort evidence cards by the direction of energy flow, justify each placement with the right kind of evidence, and choose which processes could power a warming pack or a cooling pack.

50 minsmall groupPracticeCollaborationDiscussionData analysis MS-PS1-6 · practiceMS-ETS1-2 · practice
Student PDFStudent DOCXPreview
Teacher only
Answer key PDFAnswer key DOCXKey preview
First page of A Cold Pack for the Cross-Country Kit: Define, Evaluate, Modify
Worksheet 9 · Transfer and design

A Cold Pack for the Cross-Country Kit: Define, Evaluate, Modify

I can turn a user's needs into precise criteria and constraints, evaluate four cold-pack designs against them with test data, and propose a modified design with predicted temperature, time, cost and mass.

50 minpairsExtensionEngineering designData analysisWriting MS-ETS1-1 · assessesMS-ETS1-2 · assessesMS-PS1-6 · practice
Student PDFStudent DOCXPreview
Teacher only
Answer key PDFAnswer key DOCXKey preview

Collaborative labs 3 of 3

Three different investigation approaches. Each has a teacher guide (purpose, materials with quantities, estimated cost, prep, safety, procedure, expected observations, debrief, answer key, assessment criteria, accessibility adaptations, low-cost alternative) and a student recording sheet.

First page of the Four Mystery Packets: Which Way Does the Energy Go? recording sheet
Lab 1 · Evidence-based mystery

Four Mystery Packets: Which Way Does the Energy Go?

Four unlabeled packets go into water. Which ones release energy to the surroundings, which absorb it, and which do neither, and what evidence tells you?

Groups of 41 session33 min activityEst. 20 to 35 per class of 8 groups, excluding thermometersFoam cups, 8 to 12 ozDigital thermometer or temperature probe reading to 0.1 °CStopwatch or phone timer MS-PS1-6 · practiceMS-ETS1-2 · supports
Recording sheet PDFRecording sheet DOCXPreview
Teacher only
Teacher guide PDFTeacher guide DOCXGuide preview
First page of the Build a Better Pack: Design, Test and Improve a Hot or Cold Pack recording sheet
Lab 2 · Engineering design challenge

Build a Better Pack: Design, Test and Improve a Hot or Cold Pack

Can your team build a pack that warms (or cools) by a set amount within two minutes and is still working at ten minutes, without crossing the safety, mass and cost limits, and what single change should each new prototype make?

Groups of 42 sessions85 min activityEst. 15 to 30 per class of 8 groups, excluding thermometersSnack-size zip bags (about 16 by 8 cm)Foam cups, 12 to 16 ozDigital thermometer or temperature probe reading to 0.1 °C MS-PS1-6 · assessesMS-ETS1-4 · practiceMS-ETS1-1 · supports
Recording sheet PDFRecording sheet DOCXPreview
Teacher only
Teacher guide PDFTeacher guide DOCXGuide preview
First page of the The Decision Meeting: Six Hand-Warmer Prototypes, Three Customers recording sheet
Lab 3 · Data-driven decision

The Decision Meeting: Six Hand-Warmer Prototypes, Three Customers

Given test data from six hand-warmer prototypes, which prototype should go to each of three customers with different criteria and constraints, and when none fits, which characteristics from different prototypes can be combined into a better design?

Groups of 41 session42 min activityEst. 0 to 5 per classRecording sheet with the prototype test report, the temperature-time dataset and the three customer briefsGraph paper or the graph block on the recording sheetCalculator MS-ETS1-3 · assessesMS-ETS1-2 · practiceMS-PS1-6 · supports
Recording sheet PDFRecording sheet DOCXPreview
Teacher only
Teacher guide PDFTeacher guide DOCXGuide preview

Teacher guidance

Suggested sequence (7 steps)
  1. Period 1: Presentation slides 1-8 (phenomenon, targets, energy in every reaction, system and surroundings, exothermic examples). W1 phenomenon worksheet as the opener; W2 vocabulary relationships to close.
  2. Period 2: Lab 1, the four mystery packets (one session). Students measure temperature change, classify each packet and match it to a spec sheet. Follow with slides 9-12 (endothermic reactions, the compare diagram, the cold-pack discussion, vocabulary).
  3. Period 3: Slides 13-17 (bonds pay in and pay out, conservation, the match check, energy in equations, the equation check). W4 diagram worksheet on the system boundary and the bond model; W3 reading passage for homework.
  4. Period 4: Slides 18-20 (California connection, how engineers prototype, the design cycle diagram). Lab 2 session 1: read the brief, set criteria and constraints, build and test prototype 1. W7 misconception repair if time remains.
  5. Period 5: Lab 2 session 2: prototypes 2 and 3, final justification. Slides 21-23 (prototype-data task, one-change-at-a-time discussion, criteria-versus-constraints check).
  6. Period 6: Lab 3, the six-prototype decision meeting (one session, no chemicals). W5 data worksheet and W8 collaborative evidence sort share the same reasoning and can follow or substitute.
  7. Period 7: Slides 24-26 (misconception, synthesis, exit). W6 CER as the written assessment, W9 transfer design task for students who missed Lab 2, then W10 mastery as the quiz.

Materials overview: No open flames anywhere in the chapter; the magnesium flash and the match are described, never demonstrated. Lab 1 and Lab 2 use food-grade or hardware-store reagents in teacher-measured amounts: calcium chloride pellets (ice melt or pickling grade), citric acid, baking soda, 3% hydrogen peroxide, dry yeast and table salt, with digital thermometers, foam cups, snack-size zip bags, measuring cups and goggles. Lab 3 uses printed data cards, graph paper and calculators only. A pair of commercial instant hot and cold packs makes the phenomenon a live demonstration; otherwise describe it with the numbers in the phenomenon text.

Common misconceptions (5)
“Cold is a substance that flows from a cold pack into your hand.”
Why it happens: Everyday language talks about 'the cold getting in', and the skin feels the pack as something arriving rather than something leaving.
Correction: Only energy moves, and it moves on its own from warmer matter to cooler matter. A cold pack feels cold because thermal energy flows out of your hand and into the pack, where the dissolving salt absorbs it.
“Breaking bonds releases energy, so bonds are little packages of stored energy.”
Why it happens: Phrases like 'energy stored in bonds' and 'burning releases the energy in the fuel' make it sound as if snapping a bond lets energy out.
Correction: Breaking any bond takes energy in; forming any bond gives energy out. A reaction is exothermic because forming the new bonds in the products gives out more energy than breaking the old bonds in the reactants took in. The energy is stored in the whole arrangement of atoms, not inside the bonds like water in a balloon.
“If a reaction needs heat to get started, it must be endothermic.”
Why it happens: A match, a campfire and a gas stove all need a spark or flame to begin, and the lesson's rule about reactions that need a continuous energy supply is easy to over-apply.
Correction: What matters is the net transfer. Many exothermic reactions need a small push of energy to start and then release far more than they took in, which is why a fire keeps itself going. Classify by comparing total energy in with total energy out, not by whether a start-up was needed.
“Fizzing or bubbling means a reaction is giving off energy.”
Why it happens: Fizzing looks energetic, and the most familiar gas-producing reactions (burning, fireworks) are exothermic.
Correction: Gas production and energy direction are separate questions. Citric acid with baking soda fizzes and gets cold (endothermic); hydrogen peroxide with yeast fizzes and gets warm (exothermic). Only a thermometer, or light and sound leaving the system, tells the direction.
“A pack that reaches a higher temperature will also stay warm longer.”
Why it happens: Students treat temperature as the only measure of 'how much heat' a device makes.
Correction: Temperature tells how hot; the amount of reagent and how fast it reacts set how long. A thin pouch lets air reach the iron quickly, so the pack gets hotter but burns out sooner; a thicker pouch gives a lower, longer plateau. Engineers must test time and temperature separately.
Differentiation suggestions (5)
  • Multilingual learners: Teach exo- and endo- with the gestures 'push out' and 'pull in' and keep them on an anchor chart with the words heat, light and cool; provide a bilingual glossary card for system, surroundings, criteria and constraints; let Lab 1 observations be recorded as arrows (energy out / energy in) before the English sentences.
  • Students who need more support: Give a pre-labeled time axis on the Lab 2 graph and a decision frame ('My pack reached ___ °C, the criterion was ___ °C, so next time I will change ___'); provide a word bank for the bond-model slide; reduce Lab 3 to three prototypes and one user.
  • Students ready for extension: Ask them to explain why doubling the reagent in the same water does not double the temperature rise once the water is already warm (energy losses grow with the temperature difference), to design a pack that must work twice, or to explain why photosynthesis counts as endothermic even though nothing feels cold.
  • Students who need movement or alternative output: Run the system-and-surroundings idea as a floor model with a rope boundary and students carrying energy cards in or out; accept the Lab 2 justification as a recorded one-minute pitch to the 'client'; let the synthesis be a labeled sketch instead of a paragraph.
  • Students with limited fine-motor control, low vision or chemical sensitivities: Assign the recorder or timer role so a partner handles reagents; use a digital probe thermometer with a large display or a talking thermometer; provide large-print data tables; students who cannot be near reagents complete Lab 3 and W9, which need no chemicals.
Accuracy notes: where the textbook simplifies (14)
  • Cold-pack equation (p. 179): the book writes NH₄Cl + H₂O + energy → NH₄OH + HCl (with a coefficient 2 in the figure that does not balance). Dissolving ammonium chloride does not make ammonium hydroxide and hydrochloric acid; the ionic solid separates into ammonium ions and chloride ions spread through the water. Never show the book's equation. Write the cold pack as NH₄Cl + energy → NH₄⁺(aq) + Cl⁻(aq). The placement rule on the page (energy with the reactants when it flows in, with the products when it flows out) is sound, and the iron equation 4Fe + 3O₂ → 2Fe₂O₃ + energy is balanced and a fair simplified model.
  • 'Chlorine particles' (p. 177): the particles in the cold pack are chloride ions (Cl⁻), not chlorine. Chlorine gas (Cl₂) is a different, toxic substance. Use 'chloride ions' throughout.
  • Dissolving is not a chemical reaction in the strict sense (pp. 177, 179): no new substance forms when ammonium chloride or calcium chloride dissolves; the ions separate and are surrounded by water. Many courses call dissolving a physical change. Say 'endothermic change' or 'endothermic process' for the cold pack and 'exothermic process' for calcium chloride, and point out that MS-PS1-6's own clarification statement accepts dissolving these salts as a qualifying 'chemical process' for the design task. Citric acid with baking soda and hydrogen peroxide with yeast are genuine chemical reactions.
  • Reactions that need a continuous energy supply (p. 176): the book says any reaction that must be kept heated is endothermic. As an absolute rule this is unsafe. Classify by net transfer only: exothermic reactions can need a start (the match on p. 178) and can die out if heat is lost too fast. The deck and worksheets never use 'needs heating' as the deciding clue.
  • Cooking as an endothermic reaction (pp. 176, 178): the book treats a cooking kabob as a set of endothermic reactions whose products store the absorbed energy. This is a simplified model: much of the energy from the coals warms the food and the air rather than driving reactions, and cooking involves both physical and chemical changes. The chapter uses cooking only as the book's model and does not build questions on it.
  • Fireworks (p. 174): the book says the metal particles react with oxygen in the air at the top of the flight. Fireworks carry their own oxidizer (nitrates, chlorates or perchlorates) mixed with the fuel, so the burning does not depend mainly on air. Colors come from metal compounds that give off light when hot. The chapter uses fireworks only as an example of energy leaving a system as light, sound and heat.
  • Light is energy too: when magnesium burns, the brilliant white light carries energy away from the system just as the heat does. The book's phenomenon contrasts magnesium's light with chicken changing color; the chapter treats light, sound and thermal energy all as energy leaving an exothermic system.
  • Bonds and stored energy (p. 178): breaking a bond always absorbs energy and forming a bond always releases energy; the book's concept spread says this correctly. Teach it only qualitatively (no bond energies, no enthalpy values) and avoid the phrase 'energy stored in bonds', which leads students to believe breaking bonds releases energy. Say the energy is stored in the arrangement of the atoms in the system.
  • Iron hand warmers (pp. 175, 179): real pouches also contain water, salt, activated carbon and vermiculite, and the product is a hydrated iron oxide (rust). 4Fe + 3O₂ → 2Fe₂O₃ + energy is a simplified model that leaves these out; say so if a student asks what else is in the pouch. The warming comes from the reaction with oxygen, not from rubbing.
  • Prototype temperatures (pp. 180, 181): the written report gives 28 °C for prototype A, 41 °C for prototype B, 40 °C for 4 hours after the thicker pouch, and 43 °C for 4 hours after adding more iron, with room temperature about 25 °C. The photo on p. 180 labels prototype B at 31 °C, which disagrees with the text. The chapter uses the written values and its own simulated datasets; it never asks students to read the photo.
  • What cools first in a cold pack (p. 177): the book says the air around the pack cools. Strictly, the dissolving salt first draws thermal energy from the pack's own water, which cools; the pack then absorbs energy from whatever touches it (skin, air). The room's air temperature does not drop noticeably. Teach 'energy flows from your hand into the pack'.
  • Ice packs versus instant cold packs (p. 176): a reusable gel or ice pack is chilled in a freezer and involves no reaction; an instant cold pack cools when a salt dissolves after the pack is squeezed. The chapter uses 'instant cold pack' only for the squeeze-activated kind.
  • Temperature versus thermal energy: two prototypes at the same temperature can hold different amounts of thermal energy if one has more mass, which is why a heavier pack lasts longer. The lesson's engineers measure temperature and time separately for this reason; MS-PS1-6's assessment boundary (amount, time, temperature) matches that.
  • Safety framing: the lesson describes lighting charcoal hand warmers and treating a twisted ankle. The chapter gives no procedure for lighting anything and no first-aid advice; packs appear as devices to design and test with safe reagents at teacher-measured amounts, and every hands-on lab stays under 50 °C (Lab 1's amounts keep each cup near or below 40 °C; Lab 2 stops any test at 48 °C).

Review status: reviewed · 2026-10-19 · Chemistry checked against standard values: anhydrous CaCl2 dissolving (about -81 kJ/mol) gives about +10 °C for 3 g in 50 mL and up to about +30 °C for 9 g, so the Lab 2 rule (stop at 48 °C, pilot 9 g and drop to 6 g if it reaches 48 °C) is sound; the pilot now uses the most insulation a team could add, and the bag is moved only by the teacher above 50 °C. NH4Cl, citric acid + baking soda, vinegar + baking soda and H2O2 + yeast directions and sizes verified; Lab 1 station A and C expectations and the q9 class range were tightened to physically reachable values; vinegar alternatives now say 'a few degrees'. Every numeric, multiple-choice, true/false, fill and table item in W1-W10 and Labs 1-3 re-solved. Fixed: W1 iron mass behind the 3.1 g gain (about 7 g, not 11 g); W5 q7 (B, not A, warmed fastest); W7 counts (seven errors, one correct sentence); W8 card 1 (8 g giving +24 °C, matching Lab 1/Lab 2 rates) and card 3's 3-minute criterion; W10 point total (17 + 4 = 21) and the q8 interpolation note; Lab 3 Dani design predictions now meet her 15-minute start, 70 g and $2.00 limits. Lab 3 decision matrix verified from the data: P3 for Maya, P1 for Mr. Alvarez, none for Dani; costs, masses, crossing times and cost-per-hour values recomputed and correct. Energy language: removed 'produced heat ... cold' from the phenomenon, 'burning' for the iron hand warmer, and creation-style wording; DCI and debrief text now say released to / absorbed from the surroundings, with storage in the arrangement of atoms, never in bonds that break. The textbook's NH4OH + HCl cold-pack equation was removed from W10 item 5 (replaced by a water-as-product distractor), matching the chapter rule never to show it; W2 and W8 no longer suggest demonstrating burning magnesium, and W2 notes that a little nitrogen reacts. Originality: definitions and bullets that echoed the book's 6+ word runs (exothermic/endothermic definitions, 'cooled back to room temperature within', 'from the surroundings to the system', 'on the basis of the test results') rewritten; only section titles in sourceReferences remain. Standards: caGrade added to all eight lab standards entries; MS-ETS1-1 added to the chapter and MS-ETS1-2 raised to assesses to match W9, where students write their own criteria and constraints and evaluate four designs against them. Consistency: estimatedMinutes set to the 120-minute pacing sum; slide links corrected (W2/W3 examples, Lab 1 stations, W8 not W9 for choosing a warming process); Lessons 23-24 described as a preview; W3 scaffold no longer cites photosynthesis, which the passage does not contain; W4 cold-pack boundary note now matches Labs 1-2 and the slide-5 rule that either boundary is acceptable.

Source references

Verified against the student edition of Bring Science Alive! 7th Grade Integrated (Student Edition). Printed page numbers appear in the book; PDF pages are the physical pages of the 524-page scan (printed + 36). The textbook is not reproduced on this site.

SectionPrinted pagesPDF pagesUsed for
Introduction: fireworks, the lesson question and vocabulary172, 173208, 209Lesson question, the three vocabulary terms (exothermic, endothermic, prototype) and the publisher's standards list.
1. Exothermic Reactions: system and surroundings, the burning match, charcoal and iron hand warmers174, 175210, 211System-and-surroundings boundary model, exothermic examples, the iron hand warmer that Lab 3 and the slide task model.
2. Endothermic Reactions: cooking, ammonium chloride and the instant cold pack176, 177212, 213Endothermic examples, the cold-pack mechanism (rewritten with ions), accuracy notes on continuous heating and cooking.
Key Science Concept: Reactions Release and Absorb Energy (bonds break, bonds form)178214The qualitative bond-breaking and bond-forming model on slide 13, W4 and the misconception slide.
3. Showing Energy in Chemical Equations179215The placement rule for the energy term and the iron equation; the cold-pack equation is replaced with an ion version.
4. Testing and Improving Hand Warmers: prototypes, temperature tests, time tests180, 181216, 217The design-cycle diagram, the criteria of temperature and time, and the structure of Lab 2 and Lab 3.

External references used for accuracy checks

Related chapters

Ch. 13: Atoms in Chemical ReactionsCh. 12: Identifying Chemical ReactionsCh. 15: Chemical Engineering and SocietyCh. 24: Heat, Temperature, and State Changes
← Previous chapterChapter 13: Atoms in Chemical Reactions Next chapter →Chapter 15: Chemical Engineering and Society