Physical vs. Chemical Changes
Overview
This is a self-contained, no-technology substitute packet in which students distinguish physical from chemical changes. Working alone with a pencil, students read a short original passage on physical changes (state, shape, size; no new substance), chemical changes, and the signs of a reaction (gas/bubbles, color change, temperature change, precipitate, light); study an original grayscale-safe particle-model diagram contrasting a physical change (same particles rearranged) with a chemical change (new particles); analyze an original table of six described changes and their observations; classify each as physical or chemical and justify it with the evidence; identify the strongest sign of a reaction; separate observation from inference; and write an evidence-based explanation (CER) of a borderline change. It is a paper investigation with no lab materials and no hazards. Runs in a ~50-minute standard period; a ~90-minute block adds reasoning about conservation of mass and a sealed-bag evidence-test plan.
At a glance
Course: Integrated Physics and Chemistry (Grades 9–12)
Subject: Science
Time: about 50 minutes standard, or a ~90-minute block (block adds a conservation-of-mass extension)
Materials: printed packet and a pencil (no calculator, computer, or lab materials)
Work mode: independent
Product: a data analysis and a claim–evidence–reasoning explanation (CER)
Standards (provisional): 19 TAC Chapter 112 (Integrated Physics and Chemistry) — distinguishing physical from chemical changes and recognizing evidence of a chemical reaction. Provisional — pending educator verification against the current official TAC source; no section number is asserted. Standards are paraphrased, not quoted. This packet does not claim formal alignment to the TEKS.
Accessible version of the student activity
The full student activity is reproduced below in plain, screen-reader-friendly HTML. It reflows on phones and at 200% zoom. Write your answers on the printed packet.
Start (5 minutes) — Notice & Wonder
- An ice cube melts into liquid water; a slice of bread burns into black, smoking char. Both are "changes" but feel different. Write one thing you notice and one thing you wonder about how they differ.
- In which change do you think a brand-new substance was made — something that was not there before? Give your best first idea and say what makes you think so.
Build (8–12 minutes) — Read the science
Matter changes in two ways. The key question is always: Was a new substance made? A physical change changes only the state, shape, or size — the same substance remains and no new material forms (melting, freezing, boiling, dissolving, crushing, cutting); it can usually be reversed. A chemical change (chemical reaction) turns the starting substances into one or more new substances with new properties (burning, rusting, digesting); it is usually hard to reverse.
Signs a reaction may have occurred: gas or bubbles; a color change that is not just mixing; a temperature change on its own; a precipitate (a solid appearing when two clear liquids combine); or light or a new odor. Cautions: a single sign is a clue, not proof — boiling water bubbles are just water vapor, dissolving can cool water, and mixing paint changes color without making anything new. Conservation of mass: in either kind of change, atoms are only rearranged, never made or destroyed, so the total mass stays the same (if gas escapes, the solid plus the escaped gas still equals the starting mass).
Word bank
- physical change
- a change in state, shape, or size with no new substance formed (e.g., melting, dissolving).
- chemical change
- a change that forms one or more new substances (a chemical reaction; e.g., burning, rusting).
- substance
- a single kind of matter with its own fixed properties (color, density, boiling point, etc.).
- precipitate
- a solid that forms and settles out when two liquids are combined.
- evidence
- an observation you can point to that supports a claim (a sign of change).
- conservation of mass
- total mass stays the same because atoms are only rearranged, never made or destroyed.
- Using Figure 1, describe in one sentence how you can tell from the particles whether a change is physical or chemical, using the words "same particles" and "new particles."
Apply (20–25 minutes) — Use the data
Six described changes and the observations recorded for each (original scenarios):
| # | Change described | Observations recorded |
|---|---|---|
| A | An ice cube is left on a warm counter. | The solid turns to liquid water; no bubbles, no color change; it can be refrozen into ice. |
| B | A strip of shiny iron sits outdoors for two weeks. | A flaky orange-brown layer builds up; the new coating is brittle and does not conduct or shine like the iron did. |
| C | A spoon of table salt is stirred into a glass of water. | The salt seems to disappear; the liquid stays clear; evaporating the water leaves the salt behind unchanged. |
| D | Two clear liquids are poured together. | Instantly a cloudy white solid forms and settles to the bottom; the mixture also feels slightly warm. |
| E | A birthday candle burns. | The flame gives off light and heat; wax disappears; a faint smoky odor and a little water vapor and gas are produced. |
| F | A sheet of paper is folded and torn into small pieces. | The pieces are smaller but still white paper; nothing bubbles, heats, or changes color. |
- Classify and justify: for each change A–F write P (physical) or C (chemical), then name the evidence from Table 1 you used.
- Strongest sign: in change D, two clear liquids form a cloudy solid and the mixture feels slightly warm. Which single sign — the precipitate or the warmth — is the strongest evidence of a chemical reaction, and why is the other weaker by itself?
- Trap check: a classmate says ice melting (A) and salt dissolving (C) must be chemical because "the stuff is gone." Explain why disappearing is not evidence of a new substance, pointing to the Table 1 observation that shows the substance is still the same.
- Observation vs. inference — mark O (recorded directly in Table 1) or I (a reasoned
conclusion):
- a) In change D, a cloudy white solid formed and settled to the bottom.
- b) A new substance was created when the two liquids in change D were combined.
- c) In change B, a flaky orange-brown layer built up on the iron.
- d) The rust in change B is a different substance than the iron it formed on.
- Two look-alikes: using the idea of a "new substance," explain why bubbles from boiling water are a physical change but the gas and light from a burning candle are a chemical change.
Explain (7–10 minutes) — Claim, Evidence, Reasoning
Question 9. A borderline case: a shiny silver spoon is left in a dish for a month and slowly turns dull and dark on the surface; the dark coating can be gently rubbed off, revealing shiny metal underneath, and it has a different color and dullness than the silver. Is this a physical or a chemical change? Write a claim, support it with two pieces of evidence from the description, then explain your reasoning using the idea of a new substance and its properties.
Sentence stems you may use: "This is a ____ change because…"; "One piece of evidence is…"; "A second piece of evidence is…"; "This shows a new substance formed because its properties (color / dullness) are different from…"
Block-period addition (conservation of mass): explain how a tarnishing spoon can gain a little mass while a burning candle loses mass, yet both still obey conservation of mass because atoms are only rearranged — and why you would have to trap the gases to show the total mass did not change.
Close (5 minutes) — ACE
- Articulate: explain, in your own words, the one question you ask to tell a physical change from a chemical change.
- Connect: point to one row of Table 1 whose observations give the clearest evidence of a chemical change, and name the sign.
- Extend: give a new everyday example (not in Table 1) of a chemical change and name the sign you would expect.
Continue (optional) — Early finisher & block extension
Early finisher: build a two-column "Physical / Chemical" chart with at least four changes from your own life, giving the sign or reasoning for each, and circle the one you were least sure about.
Block extension (~+30 min): design a plan, using only observation, to decide whether mixing a sealed bag's mystery solid and liquid causes a chemical change — list the signs you would watch for, explain how weighing the sealed bag before and after checks conservation of mass, and state which single observation would most convince you a new substance formed.
Turn in
Hand in the whole packet with your name, class period, and date, with questions 1–9 and the ACE box answered. Include the optional sorting table, the conservation-of-mass paragraph, and the sealed-bag plan if you did them.