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Lesson · Grade 7 · Science

Physical change or chemical change?

  • Grade 7
  • Science
  • 1 min 18 s
  • British Columbia
  • BC7-SC-17

The video builds one two-column diagram: on the left, ice melts into water and a zoom into each shows the same seven water particles, only arranged differently, so the substance is unchanged and the change is physical and easy to reverse. On the right, an iron nail rusts in damp air and the zoom shows iron particles joining with oxygen from the air to form rust, a new substance, so the change is chemical and hard to reverse, with three clue tags (new colour, gas bubbles, heat or light) before the one-line recap "Same substance: physical. New substance: chemical."

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In one sentence

The question this lesson answers

When something changes, is it a physical change or a chemical change? Let us look at two examples.

Here is some ice. Warm it, and it melts into water.

Transcript

What the lesson says

When something changes, is it a physical change or a chemical change? Let us look at two examples.

Here is some ice. Warm it, and it melts into water.

Zoom in on the particles. Each one is still a water particle, just moving more freely.

Only the form changed. It is still water, so this is a physical change.

Freeze the water and you get ice back. Physical changes are usually easy to reverse.

Now an iron nail. Left in damp air, it slowly turns to rust.

Zoom in again. The iron is made of iron particles.

Oxygen from the air joins with the iron, and the particles are put together in a new way.

Rust is a new substance. It is not iron any more, so this is a chemical change.

You cannot simply turn rust back into iron. Chemical changes are hard to reverse.

Clues for a chemical change: a new colour, bubbles of gas, or heat and light given off.

Same substance, physical change. New substance, chemical change.

Curriculum

Where this fits

British Columbia, Grade 7

Science, Chemistry: chemical changesBC7-SC-17

Previous: How Crystals FormNext: Atoms rearrange: vinegar and baking soda

The outcomes and strands follow the British Columbia curriculum.

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