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9th grade · Science · Unit 7 of 10

Chemical Change

Reactions, mass and chemical names

What your child practices

Telling a chemical change from a physical change, reading simple word and symbol equations, why mass is conserved, what speeds a reaction up, exothermic and endothermic changes, and GHS safety.

Maine Learning Results learning standard: HS-PS1-2; HS-PS1-5; HS-PS1-7 · chemical reactions, reaction rates and conservation of atoms

How we explain it

Children can open this short lesson before they practice.

  1. Signs of a chemical change: gas bubbles, a color change, a new solid, light or heat.
  2. In an equation, count atoms: the big number multiplies the whole formula; the small number counts one element.
  3. Mass is conserved. Read the hazard symbols on chemicals before using them.

Example: In 2H₂O, how many hydrogen atoms are there? Each H₂O has 2 hydrogen atoms. There are 2 molecules: 2 × 2 = 4. Answer: 4

Chemical Change in Maine

In the Maine Learning Results, this is unit 7 of 10 in 9th grade Science, after The Periodic Table and before Evolution & Selection.

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: Maine 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

    In 2H₂ + O₂ → 2H₂O, how many hydrogen atoms are on the left side (reactants)?

    answer box

  2. Question 2

    Baking soda is added to vinegar and bubbles appear. A student weighs everything in an open container before and after, and the mass goes down. Why?

    • Mass is destroyed in reactions
    • The gas that formed escaped into the air
    • The container got lighter
    • The vinegar turned into energy

  3. Question 3

    The word equation magnesium + oxygen → magnesium oxide describes…

    • magnesium burning in air
    • magnesium melting
    • water boiling
    • magnesium dissolving

  4. Question 4

    A solution of hydrochloric acid is poured on zinc, and a gas forms that burns with a small pop. What is the gas most likely to be?

    • oxygen
    • nitrogen
    • helium
    • hydrogen

  5. Question 5

    A cold pack gets cold when the chemicals inside are mixed. This is an example of…

    • a physical change only
    • an exothermic reaction
    • an endothermic reaction
    • combustion

  6. Question 6

    What is the chemical name of NaCl?

    • sodium chloride
    • nitrogen chloride
    • sodium chlorine
    • sodium chlorate

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