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8th grade · Science · Unit 9 of 10

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.

Minnesota K-12 Academic Standards benchmark: 8P.2.1.1.1; 8P.3.1.1.2 · telling when a chemical reaction happened, and atoms being conserved in a reaction

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 Minnesota

In the Minnesota K-12 Academic Standards, this is unit 9 of 10 in 8th grade Science, after Kinetic & Potential Energy and before Thermal Energy & Insulation.

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: Minnesota Department of Education (MDE)

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 physical change?

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

  2. Question 2

    An endothermic reaction…

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

  3. Question 3

    Substances made by a reaction are…

    • mixtures only
    • products
    • elements only
    • reactants

  4. Question 4

    Substances at the start of a reaction are…

    • reactants
    • solvents
    • catalysts
    • products

  5. Question 5

    Which is a chemical change?

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

  6. Question 6

    A self-heating meal pack uses a reaction. Engineers want it hotter. A good test is to…

    • paint it a new color
    • guess
    • change the amount of reactant and measure temperature
    • make the box bigger only

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