SME
Grade 7 Science · Problem type
Chemical change or physical change?
Use this for “Is water changing into steam a chemical change?”
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Did a new substance form?
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Assumptions
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Signs of a reaction: a gas that was not there, a color change, a temperature change, a solid appearing.
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A gas alone is not proof: boiling water gives a gas, but it is still water.
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Related lessons
Chemical reactions and balancing basics
Main lesson
Iron rusting: iron and oxygen make iron oxide
Use this for “How many oxygen molecules react with 4 iron atoms to make rust?”
Burning methane
Use this for “Balance CH₄ + O₂ → CO₂ + H₂O” and “How many oxygen molecules does one methane molecule burn with?”
Mass before and after a reaction
Use this for “20 g of A and 10 g of B react completely. How much C forms?” and “The sealed bottle weighed 230 g; opened, 228.5 g. How much gas escaped?”
Changes that heat up or cool down
Use this for “Which reaction could warm a meal without a flame?”