Learning targets

Georgia S8P1c — Plan and carry out investigations to compare and contrast chemical (reactivity, combustibility) and physical (density, melting point, boiling point) properties of matter.
Georgia S8P1d — Construct an argument based on observational evidence to support the claim that when a change in a substance occurs, it can be classified as either chemical or physical.
Target 1 · Physical vs chemical properties
  • I can tell a physical property (observed or measured without changing the substance) from a chemical property (how it can change into something new).
  • I can give examples of each.
Target 2 · Density, melting point, boiling point
  • I can explain why density, melting point, and boiling point are physical properties.
  • I can calculate density and use it to identify a substance.
Target 3 · Physical vs chemical changes
  • I can classify a change as physical or chemical.
  • I can list the signs that a chemical change may have happened, and say when a sign can fool you.
Target 4 · Argue from evidence
  • I can make a claim about a change and support it with observations and reasoning.

The one question

Is it still the same substance?
If you can observe it, measure it, or do it and the substance is still what it was, the property or change is physical. If finding out or doing it turns the substance into something new, it is chemical.
Left: testing if the bar is magnetic changes nothing about it. A physical property. Right: finding out if it rusts means letting it turn into rust. A chemical property.

Properties: describing what something is like

Physical properties
Things you can observe or measure without changing the substance.
  • color, luster (shininess), texture
  • hardness, malleability (can be hammered flat), ductility
  • state of matter at room temperature
  • magnetism, conductivity (heat or electricity)
  • solubility (does it dissolve?)
  • density, melting point, boiling point
Chemical properties
Describe how a substance can change into a new substance. You only find out by trying it, and afterward it is not the same stuff.
  • reactivity with water, acid, or oxygen (does it rust? tarnish? fizz?)
  • combustibility / flammability (does it burn?)
  • ability to rot or decompose
  • toxicity (how it reacts inside a living thing)
The melting-point trap. Melting point feels chemical because "the ice changed!" But when ice melts it is still H2O. Measuring a melting point never changes what the substance is, only its state. Physical. Compare: to find out if paper is combustible you have to burn it, and then it is ash and smoke, not paper. Chemical.

Sort the properties

Click a property, then click the bucket it belongs in.

Density: a substance's ID card

Density = mass ÷ volume. It tells you how much stuff is packed into each cubic centimeter. Units: g/cm3 for solids, g/mL for liquids (and 1 cm3 = 1 mL).

Density is a characteristic property: it is the same no matter how big the sample is. A gold ring and a gold bar are both 19.3 g/cm3. That is why density can identify a substance.

The killer misconception: "bigger or heavier means more dense." Cut an aluminum block in half. Each half has half the mass AND half the volume, so the density is still 2.7. A bowling ball and a beach ball are the same size, but the bowling ball is far more dense.
Sink or float: less dense than water (1.0 g/mL) floats. More dense sinks. Ice is 0.92, so it floats. Regular soda sinks and diet soda floats: dissolved sugar makes regular soda more dense.
Density calculator
SubstanceDensity (g/cm³)
Run the experiment yourself: Density Dive on the Virtual Lab Bench.

Changes: something happens to the substance

Physical change
Ice cubes melting in a glass of water
Ice melting: still water.
The substance stays the same substance. Only its shape, size, or state changes.
  • all changes of state: melting, freezing, boiling, evaporating, condensing
  • dissolving (salt in water is still salt: evaporate the water and it comes back)
  • cutting, tearing, crushing, grinding, bending, stretching
  • mixing things without a reaction
Usually easy to undo.
Chemical change
A rusty nail with a close-up of iron and oxygen atoms bonded into rust
Iron rusting: iron + oxygen became a new compound.
Atoms rearrange and a new substance forms with new properties. Also called a chemical reaction.
  • burning, rusting, tarnishing
  • baking a cake, frying an egg, digesting food
  • baking soda + vinegar fizzing
  • a glow stick lighting up, fireworks, rotting
Usually hard or impossible to undo. You cannot un-burn a match.

Evidence that a chemical change MAY have happened

Each of these is evidence, not proof. The final test is always: is there a new substance?

Gas is produced
Bubbles or fizz from a reaction.
But: boiling water bubbles too, and that is physical. The bubbles in boiling water are water vapor, not a new gas.
Unexpected color change
A silver ring turns black; a cut apple browns.
But: mixing yellow and blue paint is physical. The color change has to come from a new substance.
A precipitate forms
Two clear liquids mix and a solid appears.
But: a solid appearing because water froze is physical.
A new odor
Rotten eggs, burnt toast.
But: smelling perfume across a room is just evaporation.
Light or a temperature change on its own
A glow stick, a fire, a hand warmer, a bag that gets cold when mixed.
But: if it got hot because you put it on a stove, that is you adding energy, not a reaction. It counts when the mixture heats or cools itself.
A sealed plastic bag inflating with fizzing bubbles inside
Baking soda and vinegar in a sealed bag: gas forms, the bag inflates and gets cold. Two signs at once. And the mass on the balance does not change.
Matter is conserved
In a chemical change the atoms only rearrange. Nothing is created or destroyed, so the mass of the products equals the mass of the reactants. Open the bag and the mass drops only because the gas escaped, not because matter vanished.
Want the full version? Balancing Chemical Equations.

Evidence judge

Read the scene. Call it physical or chemical. Then pick the observations that back you up.

Build a claim-evidence-reasoning argument

This is the test question. Pick a scene, then choose the claim, check the evidence, and pick the reasoning. The paragraph writes itself below.

Claim
Evidence (check all that apply)
Reasoning

One-minute video

Simple Science: physical and chemical changes. Needs wifi.

Show the video

How are you feeling about this today?

Nothing here is graded. Switch levels any time.

Printable worksheets

Student page first, answer key on the next page. Shuffle to pull a fresh set.

Standards and targets

S8P1c — compare and contrast chemical (reactivity, combustibility) and physical (density, melting point, boiling point) properties. S8P1d — construct an argument from observational evidence that a change is chemical or physical. The evidence judge and CER builder are aimed squarely at S8P1d's argument.

  • Target 1: physical vs chemical properties with examples.
  • Target 2: density, melting point, boiling point as physical properties; D = m ÷ V and identification.
  • Target 3: physical vs chemical change; the five signs and their exceptions.
  • Target 4: claim, evidence, reasoning.

How the levels differ

Level 1 · Coach
Two choices (physical or chemical). Each item says whether it is a property or a change. The coach line restates the one question. Every answer is explained.
Level 2 · Guided
Four boxes on every item: physical property, chemical property, physical change, chemical change. Plus "which observation is evidence of a chemical change." Two hint layers.
Level 3 · Challenge
Trap items (dissolving, melting point, boiling bubbles, stove heat vs self-heating), density calculations and identification from the table, strongest-evidence, and reasoning-statement questions.

Classroom notes

  • The demo of the unit: baking soda in a sealed bag with a small cup of vinegar inside. Mass it, tip the cup, watch it inflate and get cold, mass it again. Same number. Chemical-change evidence and conservation in five minutes. Then open the bag and re-mass: open vs closed system.
  • Hold up a nail. "Tell me everything about it without changing it" (physical). "Now, what can I only find out by destroying it?" (chemical). That line is the whole lesson.
  • Say the nuance out loud: temperature change counts as evidence when the mixture heats or cools itself, not when you heat it. That is exactly what the CER test question turns on.
  • Density reps: two or three D = m ÷ V problems on the board, and the cut-it-in-half question. Units: g/cm3 for solids, g/mL for liquids.
  • Misconceptions handled on the page: melting point is chemical; bigger means denser; dissolved salt is gone; boiling bubbles are a reaction; burning destroys matter.
  • Nothing is collected. Pairs with Unit 2 guided notes Parts 3 and 4, and Density Dive on the Virtual Lab Bench.