Chemical reaction — Science definition
Defined in 2 courses:
- A process where reactants interact and rearrange into one or more new products. (Physical Science: Matter, Forces & Energy)
- A process that breaks and forms chemical bonds, changing one set of substances into another. (Life Science: Biology)
Where it is taught
- Signs of a Chemical Reaction — Chemistry, Physical Science: Matter, Forces & Energy, Grade 8
- Biochemical Reactions & Energy — Investigating the Chemistry of Life, Life Science: Biology, Grade 10
In use
A chemical reaction happens when substances called reactants interact and rearrange their atoms into new substances called products — and those products have genuinely different properties from what you started with.
Signs of a Chemical Reaction
Questions using chemical reaction
Problem 1
- Formation of a precipitate
- Gas bubbles forming
- A change of shape
- A color change
Answer and explanation
A change of shape
A change of shape alone (like bending or cutting) is a physical change, not evidence of a chemical reaction.
Problem 2
Answer and explanation
Gas bubbles suggest a new gaseous substance is escaping that wasn't there before, and a color change suggests new compounds have formed with different light-absorbing properties than the original substances.
Problem 3
- ice melting
- iron rusting
- water boiling
- sugar dissolving in tea
Answer and explanation
iron rusting
Rusting forms a new substance, iron oxide, so it is a chemical reaction — unlike the other physical changes listed.
Problem 4
Answer and explanation
Physical processes can also change temperature — for example, dissolving some substances absorbs or releases heat even though no new substance forms — so a temperature change is only a clue, not final proof.
Taught alongside
- reactant
- product
- precipitate
- model
- evidence
- system boundary
- assumption
- synthesis reaction
- decomposition reaction
- ATP
- metabolism