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8th grade Reactions that release or absorb energy worksheet

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Reactions that release or absorb energy

Grade 8 Science Worksheet

NameDate

Circle the best answer, or write your answer on the line.

  1. A hand-warmer test warms 200 g of water from 18 °C to 21 °C. Energy = mass × 4.18 J/(g·°C) × rise. How many joules did Esme's water take in?

  2. Energy is kept in this reaction. How much thermal energy do the surroundings have after the reaction, Jun?

  3. Energy is kept in Kira's reaction. How much thermal energy do the surroundings have after the reaction?

  4. A cup of reacting powder keeps its total energy. How much thermal energy is in Luz's surroundings after the reaction?

  5. Milo's card: a reaction needs a match flame to start, then keeps going by itself and the flask gets hot. Exothermic or endothermic?

    • Neither, since a flame is not a kind of energy at all
    • Exothermic: the flame only gets it started
    • Endothermic, since it needed a flame to start
    • Endothermic, since the flame gave it the energy it needed

  6. Read this first

    Energy for a burner-heated reaction (example data)

    energyamount (kJ)
    absorbed by the reaction30
    released by the reaction12

  7. A reaction goes only while a burner heats it. Overall, is it exothermic or endothermic, Noah?

    • Exothermic, since it released 12 kJ, which is real energy
    • Endothermic: it absorbs 30 kJ and releases only 12 kJ
    • Exothermic, since a burner heating it makes things hot
    • Neither, since the two energy amounts are not equal

  8. Pia's card: a reaction needs a burner to start, then keeps glowing and warming the table with the burner off. Which is it?

    • Endothermic, since it needed a burner
    • Exothermic: the burner only started it
    • Neither, since it glows
    • Endothermic, since the burner supplied the energy

  9. The water cools after its peak. What is the best reason, Ren?

    • The reaction is done releasing, and the room takes energy
    • Cold flows in from the cooler room into the water
    • The reaction turns endothermic and starts absorbing energy
    • Energy is destroyed when the water is warmer than the room

  10. What does the dip show about the reaction, and why does the water warm up again later, Tala?

    • It released energy first, then it absorbed energy later
    • It absorbed energy, then the warmer room heated the water
    • Energy was destroyed in the dip, then made again later
    • It released cold into the water, and the cold wore off

  11. Reactions A and B each warm the same amount of water from 22 °C. Which released more energy, and how can you tell, Zee?

    • A absorbed more energy, since its water got much hotter
    • The same, since both lines go up and then come down again
    • A: its water rose 10 °C above the start, B's only 6 °C
    • B, since it ended hotter: 26 °C against 25 °C at 10 min
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8th grade Reactions that release or absorb energy worksheet – printable
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About this worksheet

Reactions that release or absorb energy. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can find a temperature change as end minus start (a cooling is negative) and say what its sign means for the reaction.
  • I can read an energy bar chart: the total is kept, so the store that falls gives to the store that rises, and no energy is made.
  • I can work out the energy the water took in (mass × 4.18 J per gram per °C × rise) and the energy per gram of reactant.
  • I can say that a start-up flame or burner does not make a reaction endothermic: what counts is whether it absorbs or releases more energy overall.
  • I can read a temperature-time graph (peak, dip, later cooling or rewarming), and choose a reaction for a hand warmer or cold pack by checking the results against the target.
  • I can spot a fair-test problem (different masses of water) and a claim that cold flows.

Standard: MS-PS1-6 (partial: reading only)

Words to know

exothermic: A reaction that releases energy to its surroundings

endothermic: A reaction that absorbs energy from its surroundings

surroundings: The water, cup and air around the reaction

temperature change: End temperature minus start temperature

joule (J): A unit of energy; 1 kJ = 1000 J

energy store: Where energy sits: chemical, thermal and so on

Common mistakes

Your child subtracted the end from the start. Change is always the end minus the start, so a cooling gives a negative number.

Your child added the two temperatures. A change is found by subtracting the start from the end.

Your child swapped the meaning. Surroundings that warm up mean the reaction released energy; surroundings that cool mean it absorbed energy.

Questions parents ask

What is the most common mistake with reactions that release or absorb energy?

Your child subtracted the end from the start. Change is always the end minus the start, so a cooling gives a negative number.

Are these 8th grade science worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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