Reactions that release or absorb energy
Grade 8 Science Worksheet - Challenge Me
Circle the best answer, or write your answer on the line.
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
Hand-warmer trials starting at 22 °C (test results)
reaction highest temperature (°C) A 40 B 58 C 29 A hand warmer must reach at least 35 °C and stay under 50 °C. Which reaction fits, Jun?
- A and B, since both pass 35 °C
- B, since the hottest reaction warms hands the most
- C, since it is the safest
- A, since it reaches 35 °C and stays under 50 °C
Cold-pack trials starting at 22 °C (test results)
reaction lowest temperature (°C) P 3 Q 15 R -8 A cold pack must drop to 10 °C or lower but stay above 0 °C. Which reaction fits, Kira?
- P: it falls under 10 °C but stays above 0 °C
- 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
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.
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
- Y released more, since its water ended hotter
- Neither released energy, since the start was the same
- X released more: 100 g × 6 °C is more than 50 g × 9 °C
How much did the reaction warm the water, Milo?
- 13 °C, the rise from the start to the peak
- 3 °C, the change from the start to the end of the graph
- 34 °C, the temperature at the peak
- 10 °C, the fall after the peak
What was the biggest drop in temperature, and what caused the water to warm again, Noah?
- 9 °C, and the warmer room added energy to the water
- 15 °C, and the reaction released energy to the water
- 3 °C, from the start to the end of the graph, and the reaction released energy
- 3 °C, and the cold wore off
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 energy faster; the peaks do not show totals
- A released more total energy, since its line is steeper
- A released less energy, since it cooled sooner
- Both released exactly the same energy, since the peaks match
Ren says any reaction that needs a burner must be endothermic. What is the best reply?
- No: a burner may only start it; the net energy decides
- No: only reactions that make light are exothermic
- Yes: needing energy means the reaction absorbs energy
- Yes: a burner only heats things, so the reaction takes heat
Zee says a cold pack works by giving out cold to your skin. Which reply fits the evidence best?
- Disagree: the pack releases energy into your skin
- Disagree: the pack takes energy from your skin
- Agree: cold flows from the pack into the skin
- Agree: the pack makes cold, so it must give it out