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8th grade · Science · Unit 2 of 13

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.

Texas Essential Knowledge and Skills (TEKS) teks student expectation: 8.6(E) · conservation of mass in chemical reactions and balanced equations

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 Texas

In the Texas Essential Knowledge and Skills (TEKS), this is unit 2 of 13 in 8th grade Science, after Elements & Compounds and before Forces, Motion & Momentum.

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: Texas Education Agency (TEA)

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

    A catalyst is a substance that…

    • slows a reaction down
    • is always a gas
    • turns into a product
    • speeds up a reaction without being used up

  3. Question 3

    Which statement about a balanced chemical equation is correct?

    • Only the reactants have atoms
    • The same number of molecules always appears on both sides
    • Products always have more atoms
    • The same number of each kind of atom appears on both sides

  4. Question 4

    Which is a way to make a reaction go faster?

    • use bigger lumps instead of powder
    • make the reactants more dilute
    • raise the temperature
    • lower the temperature

  5. Question 5

    10 g of one substance reacts completely with 5 g of another in a closed container to form one product. What is the mass of the product?

    • 12 g
    • 5 g
    • 15 g
    • 20 g

  6. Question 6

    What does the law of conservation of mass say?

    • Products always have more mass
    • Mass is lost when a gas forms
    • The total mass of the reactants equals the total mass of the products
    • Mass can be created by heat

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