New Stuff: Chemical Changes
Identify signs of new substance formation.
What this lesson covers
Why it matters
A magnesium ribbon burns with a blinding flash, leaving behind a white ash that feels nothing like the metal you started with.
The idea in plain words
Match the reactants to the product: 2Mg + O₂ → 2MgO. Notice how atoms rearrange to form a new compound.
Predict first
Is the white ash simply cooled-down magnesium, or is it a brand-new substance?
Chemical changes create new substances. The white ash is magnesium oxide, chemically distinct from the original metal.
- It is new magnesium, just in a different shape
- It is a new substance, magnesium oxide, with different properties — correct
- It is burnt air
What you do
Ignite the magnesium ribbon. Observe the dazzling white light and the formation of white powder.
Check yourself
What visual evidence confirms a chemical change occurred?
The reaction produces dazzling white light and a white powder (MgO), distinct from the silvery metal.
Why is this reaction classified as a chemical change?
Chemical changes are defined by the formation of new substances, not just the input of energy.
Which equation correctly represents this reaction?
Magnesium oxide is MgO. Oxygen exists as O₂. The balanced equation is 2Mg + O₂ → 2MgO.
- The magnesium ribbon melted into a liquid
- Dazzling white light and formation of white MgO powder — correct
- The ribbon turned blue
- Because heat was applied
- Because a new substance with different properties was formed — correct
- Because the magnesium disappeared
- Mg + O₂ → MgO₂
- 2Mg + O₂ → 2MgO — correct
- Mg + O → MgO