What You Need to Know

Key Concept Diagram

A physical change alters the form or appearance of a substance without changing its chemical composition (e.g. melting, dissolving)

A chemical change produces one or more new substances with different properties (e.g. burning, rusting, cooking)

Evidence of a chemical change includes colour change, gas production (bubbling), temperature change, or formation of a precipitate

Physical changes are generally reversible (e.g. ice → water → ice); most chemical changes are not easily reversible

Key Vocabulary

Physical change

A change in the form, size, or state of matter that does not create a new substance

Chemical change

A change that produces one or more new substances with different properties from the original

Reversible change

A change that can be undone to return to the original substance (e.g. melting and freezing)

Irreversible change

A change that cannot easily be undone to restore the original material (e.g. burning)

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

Ice melting into water is an example of which type of change?

Chemical change Irreversible change Physical change Nuclear change

Question 2

Which observation is the strongest evidence that a chemical change has occurred?

The substance has been cut into smaller pieces The substance has been melted by heat The substance has dissolved in water The substance has changed colour and released a gas

Question 3

Burning wood is an example of an irreversible chemical change because:

The ash and gases produced cannot be turned back into wood The wood changes colour The wood gets smaller The wood needs heat to burn

Changes to Matter