Unit 1 · Energy & Matter in My World · Week 4
When something burns or rusts, where does the matter go (or come from)?
Steel wool on a balance gets heavier when it burns. A campfire log turns to a tiny pile of ash. Both are puzzling — what is really happening to the matter?
Start here
How we work this lesson (our expectations)
- Look closely before you conclude
- Count everything — including the air
- Challenge ideas kindly, not people
- Supports are for everyone — open any you want
30-second check-in social awareness
Today we will look at data together and build a model as a group. Before we start: think of one thing you already know about fire or rust. Share it (silently, in writing, or aloud — your choice) with a neighbor. Notice that your neighbor knows something too — curiosity looks different in every person. That shared curiosity is a scientific community.
Do-Now Quick recall
No looking back — retrieve from memory. This strengthens your brain's connections more than re-reading.
- Week 1 A hand-warmer releases energy as heat. According to what we learned, was that energy created or was it already stored somewhere? Use the word atoms or particles in your answer.
- Week 2 When energy moves from a hot object to a cold object, which direction does it flow? What word describes that direction?
- Week 3 Ice melts into water. Did the number of water molecules change? Did the type of substance change? What do we call this kind of change?
Two puzzling phenomena
Watch what happens when steel wool burns on a balance: the pan gets heavier. That is strange — shouldn't burning destroy stuff? Meanwhile, a campfire log that weighs several kilograms leaves behind only a small pile of ash. The matter seems to vanish. Both phenomena appear to break the rule we learned in Week 3 — that matter is conserved. Our question: when something burns or rusts, where does the matter go — or come from?
Steel wool on a scale gets heavier after it burns. A big log turns into a tiny pile of ash. Both are puzzling. In Week 3 we learned that matter is never destroyed. So what is really happening here? Where does the matter go — or come from?
Notice & Wonder. Write one thing you notice about either puzzle, and one thing you wonder. Hold onto your wonder — we are answering it today.
Build it From physical change to chemical change — and back to atoms
We will build understanding in three steps. Each step is small. Check your thinking after each one before moving on.
Step 1 — What makes a chemical change different from a physical change?
In Week 3 we studied physical changes: ice melts, water evaporates — the substance stays the same, only the arrangement of particles changes. A chemical change is different. When iron in steel wool reacts with oxygen in the air, the atoms rearrange and bond in a new way, forming an entirely new substance: iron oxide (the orange rust you can see). Evidence of a chemical change includes: a color change, a new substance forming, energy released or absorbed (heat, light, or both), and sometimes a gas produced. Burning wood is a chemical change because cellulose in the wood reacts with oxygen to form carbon dioxide gas and water vapor — substances with completely different properties from wood.
A physical change keeps the same substance (like melting ice — still water). A chemical change makes a brand-new substance (like burning iron — it becomes iron oxide, a completely different material). Signs of a chemical change: new color, new substance, energy released, or gas produced.
Step 2 — Why does the steel wool get heavier? (Closed-system thinking)
Here is the key idea: when the steel wool burns, iron atoms from the steel bond to oxygen atoms from the air. The scale was only measuring the steel wool at first — it was NOT measuring the oxygen in the air. Once those oxygen atoms join the iron and stay on the scale, the mass goes up. The system was not "closed" — we forgot to count the air. If you trap everything in a sealed container (a truly closed system), the total mass before and after a chemical reaction is exactly the same. The atoms do not appear or disappear; they only rearrange into new combinations. This is the Law of Conservation of Mass.
The steel wool gets heavier because it grabs oxygen atoms from the air. Those atoms are now stuck to the iron — so the total mass is more. If you could catch ALL the atoms (including the air), the mass would not change at all. Atoms never disappear or appear. They only rearrange. That is called conservation of mass.
Step 3 — Where does the log's mass go?
The log appears to almost disappear, but its atoms did not vanish — they left as invisible gases: carbon dioxide (CO₂) and water vapor (H₂O). The ash that remains is mostly minerals (ash left from inorganic compounds in the wood) that do not burn. If you could collect every molecule of CO₂ and water vapor produced, weigh it along with the ash, and compare it to the original log plus the oxygen used, the masses would be equal. Lavoisier first demonstrated this in the 1770s by burning substances in sealed flasks. Matter is conserved in every chemical reaction — the atoms are the same; only their arrangement changes.
The log's atoms leave as gases — carbon dioxide and water vapor — that you cannot see. The small ash pile is what is left of the minerals in the wood. If you could collect all the gases too, the total mass would match the original log. Nothing disappeared — the atoms just moved into the air.
Worked example — counting atoms before and after (model the reaction)
Reaction: Iron (Fe) + Oxygen (O₂) → Iron(III) oxide (Fe₂O₃) — simplified as: Fe + O → FeO (one iron atom bonds with one oxygen atom).
Before (count the atoms):
Left side: 1 iron atom (Fe) + 1 oxygen atom (O) = 2 atoms total.
After (count again):
Right side: iron oxide (FeO) — it contains 1 iron atom + 1 oxygen atom = 2 atoms total.
Result: Same atoms. Same total mass. The atoms rearranged into a new substance (FeO has different properties than iron metal), but none were created or destroyed. This is exactly what conservation of mass means at the atomic level.
Connection to Week 1: The burning reaction also releases energy (it is exothermic — heat and light come out). Where does that energy come from? It was stored in the chemical bonds, and rearranging the atoms into more stable bonds releases it — just like the hand-warmer released stored energy when particles rearranged.
Show me the atom-counting as a diagram Tier 2 · visual model
Draw two columns: Before and After. In Before, draw one square labeled Fe and one circle labeled O. In After, draw them connected (Fe–O = iron oxide). Count: 2 atoms before, 2 atoms after. Write the masses: if Fe = 56 g/mol and O = 16 g/mol, before = 72 units, after = 72 units. Same! The atoms moved together — no new atoms, none lost.
Let's use a concrete analogy first Tier 3 · re-teach
Lego analogy: You have 4 red bricks and 4 blue bricks. You build a red tower and a blue tower (physical change = rearrange). Now you pull them all apart and rebuild one red-blue striped house (chemical change = new structure). Do you have more or fewer bricks? The same number. The "substance" (the house) looks completely different, but the bricks (atoms) are the same.
Fill in: When iron burns, the iron atoms _____ with oxygen atoms to make a _____ substance. But the total number of _____ stays the same, so the total _____ is conserved.
Your turn Analyze data and build a model
Use the data below to decide whether a chemical reaction occurred and whether mass was conserved. Then build an atom model. Choose how you respond.
Data set — iron wool burning in a sealed jar
Before reaction: jar + air + steel wool. Total mass = 185.0 g. Steel wool color: silver-gray. Steel wool texture: fluffy, metallic.
After reaction: jar (still sealed, no gases escaped) + ash/oxide. Total mass = 185.0 g. Residue color: orange-brown. Residue texture: brittle, crumbles easily. A heat glow was observed during the reaction.
The task:
- Did a chemical reaction occur? Write a claim. Give at least two pieces of evidence from the data. Explain your reasoning by connecting the evidence to the definition of chemical change.
- Was mass conserved? Use the data to support your answer. Then explain why mass was conserved at the atomic level (use the word atoms).
- Draw (or describe) the atom model: Show at least 2 Fe atoms and 2 O atoms before and after the reaction. Label each atom and show how they rearranged.
I want sentence starters and a word bank Tier 2 · frames
Claim: A chemical reaction (did / did not) occur because ________.
Evidence 1: The color changed from _____ to _____, which indicates ________.
Evidence 2: The texture changed to _____, which means a _____ substance formed.
Reasoning: This is a chemical change because the _____ were rearranged into _____ bonds, creating a _____ substance with different _____.
Mass was conserved because the total mass before (_____ g) equals the total mass after (_____ g). This happened because atoms are _____ — they rearranged but were not _____ or _____.
Word bank: atoms · rearranged · new · properties · chemical change · conserved · created · destroyed · bonds · iron oxide · evidence
Let's break it into smaller steps Tier 3 · re-teach
Step A — Check for signs of chemical change (circle all that apply in the data):
Color change ✓ · New substance formed ✓ · Energy released (heat/light) ✓ · Gas produced (sealed, so none escaped but CO₂ would form in a log fire)
Step B — Compare masses: Before = _____ g. After = _____ g. Same or different? _____. This means mass was (conserved / not conserved).
Step C — Why? Count atoms in the model. If 2 Fe + 2 O go in, do you have 2 Fe + 2 O in the iron oxide? Yes. Atoms were not created or destroyed — only rearranged.
Now write one sentence for each step.
Push my thinking Extension
Antoine Lavoisier (1743–1794) — a French chemist who was also involved in tax collection and was executed during the French Revolution — showed that burning a substance in a sealed flask conserved mass. He had to invent new lab equipment to do it. Research or reason through: (1) Why was it important to seal the flask? (2) If you burned wood in an open container and measured only the solid residue, would you conclude mass was conserved? Why or why not? (3) How does the closed-system/open-system distinction connect to Week 3's physical change — do physical changes also need a closed system to show conservation?
Check yourself Did it click?
- identify evidence that a chemical reaction occurred (new substance, color change, energy released);
- explain that in a chemical reaction, atoms rearrange — they are not created or destroyed;
- use conservation of mass to explain why a burning log's atoms end up in invisible gases, not nowhere.
A student burns a small log outside (open system). The ash pile weighs far less than the original log. The student says, "Mass was destroyed when the log burned." What is the best correction?
Re-teach: closed systems and invisible gases Tier 3
When you measure mass after a fire and see less solid, you have measured only part of the system. The carbon in the log combined with oxygen from the air to form CO₂ gas. The hydrogen in the wood combined with oxygen to form H₂O vapor. Both gases are invisible and floated away. If you sealed the burning log in a large container and weighed everything — gas, ash, and all — the total mass before equals the total mass after. Atoms do not disappear; they travel into the air as new molecules. Re-read option B.
Re-teach: matter is never created — even when mass appears to increase Tier 3
The steel wool gains mass not because matter was created, but because it pulled in oxygen atoms that were already in the air. Those atoms were always there — they just moved from the air onto the steel wool. No new matter was made; existing matter rearranged. Conservation of mass means the total number of atoms stays constant, not that the scale reading for one object stays constant. If you weighed the steel wool AND the air inside a sealed jar, the total mass before and after would match exactly.
Reflect, then show what you know
Critique a model kindly relationship skills
Look at the atom model you (or a neighbor) drew for the practice task. Before you share any critique, name one thing the model does well. Then suggest one thing to make it more accurate. Use this frame: "I notice your model shows _____, which is accurate because _____. One thing to add or change might be _____ because _____." This is how scientists improve each other's models — strengths-first, specific, kind.
Exit ticket — answer on paper or in your notebook.
- New What is one piece of evidence from today's data that a chemical reaction occurred in the steel wool experiment? (Name the evidence and explain why it indicates a chemical change, not a physical change.)
- New The total mass of the sealed jar experiment was 185.0 g before and 185.0 g after burning. Explain why mass was conserved using the word atoms.
- Spiral · Week 2 Burning steel wool releases heat and light. Using what you know about energy direction (from Week 2), is this reaction exothermic or endothermic? How do you know?
- Spiral · Week 3 A physical change (like melting ice) also conserves mass. How is that similar to what happens in a chemical change? How is it different? Use the word atoms in your answer.
- Transfer → Week 5 Next week you will design a device that uses a chemical change to release or absorb heat for a real user (like a hand warmer or a cold pack). Based on today's lesson, which type of reaction — exothermic or endothermic — would you want for a hand warmer? What question would you need to investigate to design it?
Educator panel — facilitation, accommodations, answer key
At a glance
Standards: NGSS MS-PS1-2 (analyze and interpret data on properties before/after interaction to determine if a chemical reaction occurred); MS-PS1-5 (develop a model that when atoms rearrange in a chemical reaction, mass is conserved because atoms are not created or destroyed). 3D: SEP Analyzing & Interpreting Data + Developing & Using Models · DCI PS1.B Chemical Reactions + PS1.A Structure of Matter · CCC Energy & Matter. Throughline: extends the Week 3 conservation-of-matter finding from physical to chemical change; closes the loop on the Week 1 energy-release phenomenon (exothermic bonds).
Materials (optional, fully digital-capable): Steel wool + balance (demo); sealed jar + candle or matches (demo); student notebook. The lesson works entirely without physical materials using the embedded scenario and data set. Do not let students handle burning materials without direct adult supervision and appropriate safety gear.
Facilitation arc (Rosenshine)
- Post both phenomenon images before class — let students see and react (2 min).
- Do-Now retrieval: spiral from Weeks 1–3 to surface prior knowledge (3 min).
- Launch phenomenon: "Which one surprises you more?" — cold call, quick pair-share (3 min).
- Build Steps 1–3 with the worked example; pause after each step for a quick whole-class check ("thumbs — can you explain this in one sentence?") (15 min).
- Differentiated practice — circulate and note which supports students open; use that data to identify students who may need Tier 2/3 intervention (15 min).
- Self-check + branching re-teach for option A/C/D responders (5 min).
- Brain break + model critique protocol (5 min).
- Reflection + exit ticket — exit ticket items 3–4 are spiral; item 5 previews Week 5 design challenge (7 min).
Pedagogical notes
- The "closed system" insight is the conceptual core. Students nearly always interpret the steel wool gaining mass as "magic" until they realize the scale wasn't measuring the air. Push this hard: "What did we forget to count?"
- Lavoisier connection: For enrichment, mention that before Lavoisier's 1770s experiments, the dominant theory was "phlogiston" — an invisible substance thought to be released during burning. His sealed-flask experiments disproved it by showing mass was conserved. Science changed by careful data collection, not by assumption.
- Energy throughline: This lesson explicitly connects to Week 1 (exothermic energy release). Ask students: "Week 1's hand-warmer also released energy — was that also a chemical change?" (No — sodium acetate crystallization is a physical change. The energy came from the crystal structure, not from forming new substances. This is a great contrast.)
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); simplified toggle shortens length. |
| Reduced reading load | "Reading: Simplified" swaps all core passages to shorter, plainer text site-wide. |
| Chunking / extended time | Lesson is in three numbered build steps; progress saves to localStorage. Students can stop and resume. |
| Sentence frames / word bank | Tier-2 support panel provides CER frames and a 10-word word bank. |
| Concrete analogies | Tier-3 Lego analogy + cloze sentence for atom rearrangement. Offer physical Lego bricks if available. |
| Alternative response mode | Students may draw the atom model, speak/record, or write the CER — all equally valid. |
| Behavior / focus (504, ADHD) | Named PBIS expectations; 30-sec SEL check-in; built-in movement brain break; predictable 3-step structure. |
| Multilingual / EL | Simplified text; visuals carry meaning; word bank; home-language atom model drawing is accepted and valued. |
| Safety / anxiety (re: fire) | The phenomenon is described and illustrated, not demonstrated in-class unless appropriate. Students who are uncomfortable with fire imagery may use only the rust/iron-oxide framing throughout. |
Exit ticket answer key
- Evidence of chemical change: Color changed from silver-gray to orange-brown (new substance — iron oxide — has different properties); OR a heat glow was observed (energy released). Either qualifies. Reasoning: these are properties of a new substance, not just a rearrangement of the same substance's particles (which would be physical change).
- Mass conserved: 185.0 g = 185.0 g. Reason: atoms from the steel wool and atoms from the air (oxygen) rearranged into iron oxide, but no atoms were created or destroyed — so the total count, and therefore the total mass, stayed the same.
- Exothermic: Energy flowed outward — heat and light were released to the surroundings. In an exothermic reaction, energy moves from the chemical system to the environment. (Week 2: energy flows from hot to cold, i.e., from the reaction to the cooler surroundings.)
- Similar: In both physical and chemical changes, atoms/particles are conserved — none are created or destroyed, so total mass is unchanged. Different: in a physical change, the atoms/molecules stay the same substance (water stays water); in a chemical change, atoms rearrange into entirely new substances with different properties (iron becomes iron oxide).
- Exothermic reaction for a hand warmer (energy releases into surroundings = warmth). Students should note they need to investigate which chemical reactions are exothermic, how much heat is released, whether it is safe, and whether it can be controlled or reused. (Accepts any reasonable question — the goal is previewing Week 5's design thinking.)
Why it's designed this way
Phenomenon-first with two competing puzzles forces genuine cognitive dissonance (NRC 2012; Reiser et al. 2021). The worked example fades support across the atom-counting model (Sweller, van Merriënboer); CER frames are universally available but not prescriptive (UDL 3.0). The Do-Now spirals Weeks 1–3 (Roediger & Karpicke; Rohrer) and the exit ticket continues the interleaved pattern. The "critique a model kindly" SEL protocol teaches relationship skills within the science practice of developing and using models (CASEL; NGSS SEP). The branching self-check has four options targeting the two most common misconceptions — "mass destroyed" and "new matter created" — plus a correct answer and a distractor that conflates chemical and physical change (Black & Wiliam). The closed-system scaffolding in Tier 3 directly addresses the documented student misconception that reactions can create or destroy mass (Driver et al., 1994).