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7th grade · Science · Unit 7 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.

Alaska content standards learning standard: MS-PS1-2; MS-PS1-5; MS-PS1-6 · properties change in chemical reactions, atoms are conserved, and reactions can release or absorb energy

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 Alaska

In the Alaska content standards, this is unit 7 of 10 in 7th grade Science, after How Plants Work and before Earth's Moving Surface.

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: Alaska Department of Education and Early Development

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

    Substances at the start of a reaction are…

    • reactants
    • products
    • catalysts
    • solvents

  2. Question 2

    An exothermic reaction…

    • releases thermal energy
    • absorbs thermal energy
    • releases no energy
    • makes things colder only

  3. Question 3

    Which is a sign of a chemical reaction?

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

  4. Question 4

    A chemical reaction forms…

    • new substances
    • only a new shape
    • only a new state
    • nothing new

  5. Question 5

    Which is a physical change?

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

  6. Question 6

    Wood burns in an open fire and the ashes weigh less than the wood. Why?

    • The wood was magic
    • Ash is lighter than air
    • Gases escaped into the air
    • Mass was destroyed

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