Rocket walks into the kitchen holding a banana with brown spots. "Chemical change," he says. "New stuff formed. Right?"
Raven looks up from the Bench Log. "What do you notice about the brown parts? They are not banana colored anymore."
"Color change, clue one," Rocket says. "And a bicycle left in the rain. Rust. Clue one again."
Nova hovers near the window, where steam from the kettle is fogging the glass. "And this?" she asks. "The water on the glass?"
Rocket pauses. "Steam turning back into water. Same stuff. Physical."
Raven writes three lines in the log and smiles. "You are getting fast at this."
"Fast and careful," Rocket says. "Check the properties."
Iron combines with oxygen in the presence of water to form rust. Rust is a different kind of matter from the iron, oxygen and water that made it.
A banana turning brown is a chemical change. New, darker substances form.
Cooking food, digesting food and food rotting are chemical changes. So is all burning.
Flammability, the ability to burn, is a chemical property. A chemical property describes the ability of a substance to undergo a specific chemical change.
Wax melting, sugar dissolving in a drink and steam condensing into liquid water are physical changes.
Grinding a solid into a powder is a physical change too, even though the powder may look a little different in color.
In each case, the state, form or properties change, but the chemical identity of the substance stays the same.
| Change | Clue | Verdict | Why |
|---|---|---|---|
| Iron rusting | Color change, new reddish solid | Chemical | Rust is a different kind of matter from iron |
| Banana browning | Color change | Chemical | New, darker substances form |
| Steam condensing on a window | Energy released | Physical | Still water |
| Sugar dissolving | Sugar seems to vanish | Physical | Still sugar, hidden among the water particles |
| Wood burning | Light, warmth, gas | Chemical | Burning always makes new substances |
| Week review | True or false? |
|---|---|
| A physical change keeps the identity of the substance. | ? |
| A chemical change produces one or more new substances. | ? |
| Bubbles always prove a chemical change. | ? |
| Melting point and boiling point can identify a substance. | ? |
| Cooking food is a physical change. | ? |
When baking soda and vinegar fizz, a gas leaves the cup. Does the cup get lighter? Does matter disappear?
Next week you will seal the reaction in a bag and put it on a scale. Nothing is lost, and you will prove it.
Strong week, Bench scientist. Tomorrow is Bench Day: a family change hunt.