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8th grade · Science · Unit 1 of 9

Chemical Reactions

New substances form, and atoms are conserved.

What your child practices

Practices signs of chemical reactions, how properties change when new substances form, conservation of mass, and devices that release or absorb thermal energy through reactions.

Arizona Academic Standards learning standard: 8.P1U1.1 · atoms rearranging in chemical reactions

How we explain it

Children can open this short lesson before they practice.

  1. Signs of a chemical reaction: a new color, gas bubbles, a new solid, light, or heat given off or taken in.
  2. Reactants are what you start with; products are the new substances made.
  3. Atoms are only rearranged, so the total mass stays the same.

Example: 20 g of reactants react in a sealed bag. What is the mass of the products? No atoms are lost or gained. Mass is conserved. Answer: 20 g

Chemical Reactions in Arizona

In the Arizona Academic Standards, this is unit 1 of 9 in 8th grade Science, before Mixtures & Solutions.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Arizona Department of Education

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Which is a sign of a chemical reaction?

    • Water is poured
    • Paper is cut
    • A gas forms
    • Ice melts

  2. Question 2

    Which is a physical change?

    • Melting butter
    • Burning wood
    • Baking a cake
    • Rusting iron

  3. Question 3

    An endothermic reaction…

    • releases thermal energy
    • absorbs thermal energy
    • makes light only
    • has no products

  4. Question 4

    Which is a chemical change?

    • Burning a candle wick
    • Freezing juice
    • Breaking glass
    • Dissolving sugar

  5. Question 5

    Baking soda and vinegar fizz. The bubbles are…

    • carbon dioxide gas
    • air from the room
    • oxygen from the sun
    • water vapor only

  6. Question 6

    Silver tarnishing black is a…

    • chemical change
    • physical change
    • change of state
    • mixture

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