Unit 1 · Energy & Matter in My World · Week 2
Why does an ice pack get COLD?
You squeeze an instant cold pack — no freezer, no ice cubes — and it turns cold enough to ice an injury within seconds. Where does the cold come from?
Start here
How we work this lesson (our expectations)
- Wonder out loud — questions are the work
- Use evidence, not guesses
- Reasoning > being first or fastest
- Supports are for everyone — open any you want
Partner launch relationship skills
Turn to a partner. Each of you answers this question out loud in one sentence: "What did you learn last week about where warmth comes from?" Then compare your answers — do they match, or are there differences? You are practicing the scientist move of checking your model against someone else's. There is no wrong answer right now.
Do-Now Quick recall
Pull from what you already know — no looking back. Retrieval makes ideas stick.
- Last week we said heat is really the motion of particles. In your own words: what happens to particles when something gets warmer?
- A hand-warmer releases stored energy as heat. What do we call that kind of energy release — energy going out of a process into the surroundings?
- Last week's exit ticket asked: if you pressed an ice pack against your hand, which direction would energy move — into your hand or out of it? Write your prediction now, before you see the phenomenon.
The phenomenon
A trainer on the sideline hands you a flat white packet. You squeeze it hard, feel a small pop, and shake it once. Within seconds the packet turns icy cold in your palm — cold enough to numb a twisted ankle. There is no ice inside, no refrigerator, no battery. Just a dry powder and a small pouch of water. When the inner pouch breaks, the powder dissolves, and the whole pack chills. Our question: where does the cold come from — and what does this have to do with last week's hand-warmer?
You squeeze a flat packet. A pouch inside pops, powder mixes with water, and the pack turns cold. No ice. No freezer. The cold happens from chemistry. Where does the cold come from?
Notice & Wonder. Write one thing you notice about the cold pack and one thing you wonder. Hold onto your wonder — this lesson answers it, and it also answers last week's exit-ticket prediction.
Build it Two big ideas, one small step at a time
We build the answer in steps, connecting to what you already know from Week 1. After each step there is a quick check before we move on.
Step 1 — Review: exothermic processes release energy
Last week the hand-warmer was an exothermic process: the chemical change released stored energy into the surroundings as heat. "Exo-" means outside — energy came out of the process and warmed things around it. The particles in your hand and in the air near the pouch sped up because they absorbed that released energy. We felt warmth.
Last week: the hand-warmer was exothermic — energy went out of the process. That's why it felt warm. Particles near it sped up.
Step 2 — Endothermic processes absorb energy from the surroundings
The cold pack works in the opposite direction. When ammonium nitrate (the powder) dissolves in water, the dissolving process needs energy to pull the powder particles apart and spread them through the water. It takes that energy from the water molecules and from your hand — the surroundings. "Endo-" means inside — energy goes into the process. As energy leaves the water and your hand, their particles slow down. Slower particles = lower temperature. The pack feels cold not because cold is flowing in, but because thermal energy is flowing out of your hand into the dissolving process.
The cold pack is endothermic — energy goes into the process from the surroundings. Energy leaves your hand. Your particles slow down. Slower = colder. Cold is not a thing that flows in — it is the absence of thermal energy that flowed away.
Worked example — modeling energy direction (watch how an expert reasons)
The key question to ask: which direction does energy move?
Hand-warmer (exothermic): stored energy → out of process → into surroundings → your hand warms (arrows point outward from pack).
Cold pack (endothermic): energy in surroundings (your hand, the water) → into the dissolving process → particles in hand slow down → your hand cools (arrows point inward toward pack).
What stayed the same: in both cases, energy was conserved — it was never created or destroyed, only transferred. The only difference is the direction of transfer. Energy leaving your hand doesn't vanish; it is now stored in the newly separated ammonium and nitrate particles floating in the water solution.
Show me an energy-direction diagram Tier 2 · visual
Draw two side-by-side boxes. Label the left box "Hand-warmer: exothermic." Draw arrows pointing out of the box toward the edges (energy leaving). Label the right box "Cold pack: endothermic." Draw arrows pointing in toward the center (energy entering from surroundings). Both obey the same rule: energy moves, it does not appear or disappear. The direction is what changes.
Your turn Explain where the cold comes from
Use a Claim–Evidence–Reasoning model to answer our question. Choose how you respond — all are equally valid.
The task: Where does the cold come from? Make a claim about energy direction, give evidence from the phenomenon and from what we built, and explain your reasoning using the words endothermic, energy transfer, and particles.
I want sentence starters Tier 2 · frames
Claim: The cold pack feels cold because energy ________ (direction) from ________ into ________.
Evidence: I know this because when the powder dissolved, the water and my hand ________, which means their particles ________.
Reasoning: This is an endothermic process because ________. The energy was not destroyed — it ________.
Word bank: endothermic · exothermic · absorbs · releases · transfers · particles · slows down · speeds up · surroundings · dissolving · conserved
Let's make it concrete first Tier 3 · re-teach
Analogy: Imagine a sponge dropped into a puddle. The sponge absorbs the water — the puddle gets smaller. Energy works the same way. The dissolving cold pack is the sponge. Your hand (and the water in the pack) is the puddle. The sponge absorbs thermal energy from its surroundings. The puddle doesn't gain a new substance — it just has less water. Your hand doesn't gain "cold" — it just has less thermal energy.
Fill in: The cold pack is like a sponge because it ________ energy from ________. This makes the pack feel cold because its surroundings have ________ thermal energy than before.
Now say your answer out loud before you write it. One sentence is enough.
Push my thinking Extension
Ammonium nitrate dissolving is endothermic — it absorbs energy. But if you burned ammonium nitrate, it would be exothermic — it releases far more energy than the dissolving absorbs. Using what you know about energy, particles, and chemical processes: why might the same substance behave differently depending on whether it dissolves or burns? What does that tell you about where energy is being stored and released in each process? Design a way you could test whether a mystery powder is endothermic or exothermic when dissolved in water, using only materials in a typical classroom.
Check yourself Did it click?
- explain that "cold" is not a substance that flows in — it is thermal energy flowing out;
- describe an endothermic process as one that absorbs energy from its surroundings;
- use a particle model + energy-direction arrows to show why the cold pack gets cold;
- contrast exothermic (Week 1) and endothermic (Week 2) using energy direction.
When the instant cold pack activates, where does the cold come from?
Re-teach: endothermic and the direction of energy transfer Tier 3
Key principle: cold is the absence of thermal energy, not a thing that flows. When the cold pack activates, the dissolving reaction needs energy to pull the powder particles apart. It takes that energy from the molecules around it — the water and your hand. Those molecules slow down. Slower molecules = lower temperature = feels cold. Energy was transferred, not created or destroyed. Re-read option B — it says exactly this. Draw the energy arrows pointing inward toward the pack to see it visually.
Reflect, then show what you know
Reflection metacognition + SEL
Look back at your Do-Now prediction: did you predict the correct direction of energy transfer for the cold pack? Whether you were right or wrong, what was the one idea that most changed or sharpened your thinking today? Scientists value updating their thinking with new evidence — that is not failure, that is science.
Exit ticket — answer on paper or in your notebook.
- New In your own words, what does endothermic mean? Use the phrase "energy direction" in your answer.
- New Draw and label an energy-direction diagram for an instant cold pack: show where energy starts, where it ends up, and what happens to the particles it left behind.
- Spiral From Week 1: what is heat in terms of particles? (One sentence — no notes.)
- Spiral Compare the hand-warmer (Week 1) and the cold pack (Week 2): what was the same about both, and what was opposite?
- Transfer A popsicle sits on a plate and melts. Is energy flowing into the popsicle or out of it? Where does the popsicle "go" — the matter doesn't disappear, so where is it? Use energy and particles to explain.
Educator panel — facilitation, accommodations, answer key
At a glance
Standards: NGSS MS-PS1-6 (design a device using a chemical process that releases or absorbs thermal energy — this lesson builds the conceptual prerequisite: understanding that dissolving can be endothermic); MS-PS3-3 (apply scientific principles to design a device that minimizes or maximizes thermal energy transfer — the cold pack is the exemplar device). 3D: SEP Developing & Using Models · DCI PS1.B Chemical Reactions & PS3.A Energy · CCC Energy & Matter. Throughline: the direct mirror of Week 1 — exothermic vs. endothermic completes the energy-direction conceptual pair that anchors the whole unit.
Materials (optional, fully digital-capable): one instant cold pack to activate as a demo (ammonium-nitrate type; widely available); student notebook. No lab required. The SVG diagram in the phenomenon section carries the visual model when a physical demo is unavailable.
Connection to Week 1: the Do-Now retrieval item 3 directly asks students to revisit their exit-ticket prediction from Week 1. This lesson is the explicit answer. Name this connection aloud: "Last week you predicted. Today you find out."
Facilitation arc (Rosenshine)
- Partner launch: brief retrieval + relationship-skills move before any new content (3 min). Listen for misconceptions — "cold flows in" is the dominant one.
- Do-Now retrieval while taking attendance; have 2–3 students share item 3 prediction (3 min).
- Activate the cold pack (or display the SVG). Pause before naming anything. Let students notice and wonder (2 min).
- Build Steps 1–2 with the worked example; stop and check after Step 2 — have students draw energy arrows before moving on (12 min).
- Differentiated CER practice — circulate; prompt any student writing "cold flows in" with: "What actually moves — matter or energy?" (12 min).
- Self-check + re-teach branch for any "A/C" responders (5 min).
- Brain break (evaporation observation), reflection, exit ticket (10 min).
IEP / 504 accommodation cards
Common accommodations mapped to this lesson
| Accommodation | How it's already built in / what to do |
|---|---|
| Text read aloud | Every passage has a Listen button (TTS); the simplified toggle shortens it. The phenomenon text and both Build steps have both standard and simplified versions. |
| Reduced reading load | "Reading: Simplified" swaps in shorter plain-language text site-wide. |
| Chunking / extended time | Lesson is in small steps with checks; progress saves automatically — students can stop and resume. The exothermic review (Step 1) is kept brief to reduce working-memory load before the new concept. |
| Sentence frames / word bank | Tier-2 panel under the practice task provides full CER frames plus a 10-word word bank. |
| Concrete manipulatives / models | Tier-3 "sponge in a puddle" analogy + cloze. Offer the physical cold pack to hold. The inline SVG diagram carries the particle-motion model with aria-label for screen readers. |
| Alternative response mode | Students may draw the energy-direction diagram, speak/record, or write the CER — all accepted. |
| Behavior / focus (504, ADHD) | Named expectations (PBIS), partner launch check-in, brain break with a tactile evaporation observation to ground attention before the exit ticket. |
| Multilingual / EL | Simplified text, the visual SVG model carries meaning independently of text, word bank is available in Tier-2 support, home-language reflection is allowed. |
Exit ticket answer key
- Endothermic means a process absorbs (takes in) energy from its surroundings. Energy direction: from surroundings → into the process.
- Diagram should show: arrows pointing from hand/water toward the pack's interior; label "thermal energy" on the arrows leaving the hand; label "particles slow down" on the hand side; label "dissolving reaction absorbs energy" on the pack side. Award full credit for correct arrow direction even if labels are minimal.
- Heat is the motion (jiggling) of particles — faster motion = warmer temperature.
- Same: energy was conserved (not created or destroyed); energy transferred between the pack and surroundings; particles in the surroundings changed speed. Opposite: hand-warmer = exothermic (energy out of pack, surroundings warmed, particles sped up); cold pack = endothermic (energy into pack, surroundings cooled, particles slowed).
- Energy flows into the popsicle from the warm room air and the warm plate — endothermic (melting absorbs thermal energy). The popsicle "goes" into the liquid water/juice on the plate — the matter changed state (solid → liquid) but did not disappear; the same particles are now in a less-ordered arrangement. (Previews Week 3: state changes as energy-transfer events.)
Why it's designed this way
This lesson is the intentional mirror of Week 1, exploiting the interleaving effect (Rohrer & Taylor 2007): presenting contrasting cases (exothermic vs. endothermic) in adjacent lessons rather than a single session improves discrimination learning more than massed practice on one type. The Do-Now directly retrieves Week 1 content before introducing the contrast, activating prior knowledge (Ausubel) and reducing new cognitive load. The "cold flows in" misconception is specifically targeted by the self-check distractor and the re-teach panel (research: Bransford, Brown & Cocking 2000; the "cold as substance" alternative conception is among the most persistent in middle-school thermal physics). The partner launch is a CASEL relationship-skills move and also serves as a low-stakes retrieval practice event (social recall is often stronger than solitary recall — see Weldon & Bellinger 1997). The brain break doubles as a concrete endothermic demonstration (evaporative cooling) that directly reinforces the lesson's conceptual core — brain breaks that are content-adjacent rather than purely physical produce better post-break engagement (Howie & Pate 2012). The transfer exit-ticket item (popsicle melting) previews Week 3's state-change content and begins the cross-lesson interleaving chain.