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8th grade · Science · Unit 7 of 16

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.

Alabama Course of Study content standard: 8.6; 8.8 · chemical changes and balancing atoms so mass is conserved

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 Alabama

In the Alabama Course of Study, this is unit 7 of 16 in 8th grade Science, after Chemical Reactions and before Speed, Velocity & Motion Graphs.

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: Alabama State Department of Education (ALSDE)

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 a chemical reaction, what are the reactants?

    • the energy released
    • the new substances formed
    • the starting substances
    • the container

  2. Question 2

    Rusting of iron needs which substances?

    • only nitrogen
    • only carbon dioxide
    • helium and sand
    • oxygen and water

  3. Question 3

    In CH₄ + 2O₂ → CO₂ + 2H₂O, how many oxygen atoms are on the left side (reactants)?

    answer box

  4. Question 4

    2 g of one substance reacts completely with 2 g of another in a closed container to form one product. What is the mass of the product?

    • 5 g
    • 9 g
    • 1 g
    • 4 g

  5. Question 5

    In the word equation methane + oxygen → carbon dioxide + water, which are the products?

    • oxygen and carbon dioxide
    • methane and oxygen
    • carbon dioxide and water
    • methane and water

  6. Question 6

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

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

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