Grade 8 · Science

8th grade Reactions that release or absorb energy worksheet

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Reactions that release or absorb energy

Grade 8 Science Worksheet - Challenge Me

NameDate

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

2 g of powder reacts and warms 100 g of water from 22 °C to 27 °C. Energy = mass × 4.18 × rise. How many joules were released per gram of powder, Ari?
Bo's test burns 4 g of fuel and warms 50 g of water from 20 °C to 28 °C. Energy = mass × 4.18 × rise. How many joules per gram of fuel?
A hand-warmer mix of 4 g warms 200 g of water from 21 °C to 24 °C. Energy = mass × 4.18 × rise. How many joules per gram of mix did Esme find?
Read this first
Cold-pack trials starting at 22 °C (test results)
reaction lowest temperature (°C)
P 3
Q 15
R -8
4.
A cold pack must drop to 10 °C or lower but stay above 0 °C. Which reaction fits, Kira?
- Q, since a small drop is the safer choice for a pack
- R, since the coldest pack cools the skin the most
- P and R, since both drop below 10 °C so both work
- P: it falls under 10 °C but stays above 0 °C
Use this
Investigation card (test results). Changed: the reaction and the mass of water. Measured: temperature rise (°C). Kept the same: start 20 °C. Reaction X, 100 g of water, rose 6. Reaction Y, 50 g of water, rose 9.
5.
Luz says Y released more energy, since Y's water ended hotter. What does mass × rise show?
- They released the same, since both warmed the water
- Neither released energy, since the start was the same
- X released more: 100 g × 6 °C is more than 50 g × 9 °C
- Y released more, since its water ended hotter
6.
How much did the reaction warm the water, Milo?
- 3 °C, the change from the start to the end of the graph
- 34 °C, the temperature at the peak
- 13 °C, the rise from the start to the peak
- 10 °C, the fall after the peak
7.
What was the biggest drop in temperature, and what caused the water to warm again, Noah?
- 3 °C, from the start to the end of the graph, and the reaction released energy
- 9 °C, and the warmer room added energy to the water
- 3 °C, and the cold wore off
- 15 °C, and the reaction released energy to the water
8.
Reactions A and B warm the same water to the same peak, but A rises much faster. Which statement is best supported, Pia?
- A released more total energy, since its line is steeper
- A released energy faster; the peaks do not show totals
- Both released exactly the same energy, since the peaks match
- A released less energy, since it cooled sooner
9.
Tala says burning wood is endothermic, since it needs a match first. Which reply fits the evidence best?
- Disagree: burning releases far more energy than the match
- Agree: it needed the match's energy before it burned
- Agree: the match supplies the energy that the wood absorbs
- Disagree: the wood stays cold the whole time it burns
10.
Zee says a cold pack works by giving out cold to your skin. Which reply fits the evidence best?
- Agree: the pack makes cold, so it must give it out
- Disagree: the pack takes energy from your skin
- Agree: cold flows from the pack into the skin
- Disagree: the pack releases energy into your skin

reaction	lowest temperature (°C)
P	3
Q	15
R	-8

8th grade Reactions that release or absorb energy worksheet – printable — Print: 1 2 3 4 5 6

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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