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7th grade · Science · Unit 9 of 14

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.

New York State Learning 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 New York

In the New York State Learning Standards, this is unit 9 of 14 in 7th grade Science, after Density & Buoyancy and before Earth's Changing 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: New York State Education Department (NYSED)

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?

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

  2. Question 2

    A color change when two clear liquids mix may show…

    • a chemical reaction
    • a change of state
    • evaporation
    • only mixing

  3. Question 3

    Which is a chemical change?

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

  4. Question 4

    In a chemical reaction, the total mass…

    • disappears
    • always decreases
    • always increases
    • stays the same

  5. Question 5

    Which is a physical change?

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

  6. Question 6

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

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

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