Lesson 1 of 8
Physical and chemical changes
Goal: Tell a chemical change from a physical change.
In a chemical change a new substance is made. In a physical change no new substance is made.
Physical changeMelting, boiling, dissolving, breaking. It is still the same substance, and you can usually change it back.
Chemical changeBurning, rusting, cooking. A new substance is made, and it is usually hard to change back. Another name for it is a chemical reaction.
Swipe to see three signs of a chemical reaction.
A gas is given off
Bubbles or fizzing show that a gas is being made.
Magnesium fizzes in acid. The gas is hydrogen.
The colour changes
Shiny grey iron slowly turns orange-brown.
Rust is a new substance.
Energy is given out or taken in
Burning magnesium gives out heat and a bright white light.
Some reactions take energy in, and feel cold.
- A solid can appear. When two clear solutions react and make a solid, the solid is called a precipitate.
- Signs are clues, not proof. Boiling water bubbles, but the bubbles are only water as a gas. No new substance is made.
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Key words in this lesson
Chemical reaction A change in which a new substance is made
Physical change A change in which no new substance is made