Grade 7 · Physical and Chemical Changes · Chemical Changes
Physical vs Chemical Changes
Deciding from evidence whether a new substance has formed.
Learning objectives
- Distinguish physical from chemical changes.
- Identify evidence that a chemical reaction has occurred.
- Interpret data on properties before and after a change.
NGSS alignment
MS-PS1-5
Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.
MS-PS1-3
Gather and make sense of information to describe that synthetic materials come from natural resources and impact society.
MS-PS1-2
Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion C — Processing and Evaluating
ENGAGE
Rusting or wet?
EXPLAIN
Evidence for a chemical change
- Colour change that cannot be reversed
- Gas produced (bubbles without boiling)
- Temperature change without heating or cooling
- New solid (precipitate) formed
- Different properties, such as melting point or density, before and after
Careful
Bubbles alone are not proof: boiling water bubbles too, and that is a physical change.
Practice questions
0/2 correct
Level 1
Which observation is the strongest evidence that a chemical reaction has occurred?
Level 2
Melting candle wax is a physical change because...
Reflect & track
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