Irreversible Changes
Explain that some changes result in the formation of new materials and are not usually reversible, such as burning, rusting, and reactions with acid
What a learner can do afterwards
- Define an irreversible change as one that creates new materials that cannot be changed back
- Give at least three examples: burning, rusting, mixing bicarbonate of soda with vinegar
- Describe observable signs of irreversible change: gas produced, colour change, heat given off, new substance formed
The lesson
You already know that some changes can be undone, like ice melting back into water. An irreversible change is different. It makes a brand new material, and nothing can turn that material back into what it was before.
Leave an iron nail out in the rain for a few weeks. It turns orange and flaky. That orange material is called rust, and it is a completely new substance. No amount of scrubbing turns rust back into shiny iron.
Now think about mixing bicarbonate of soda with vinegar in a bowl. As soon as they touch, the mixture fizzes and bubbles rush to the surface. That fizzing is a sign that a new gas has formed. You cannot pour the fizzing back into two separate, calm liquids ever again.
Look for these clues to spot an irreversible change: gas or bubbles appearing, a colour change, heat given off, or a brand new material forming. If you see one of these, the change is probably permanent.
An irreversible change makes a new material, and there's no way to turn it back.
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Where it sits
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Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.