Reactions that release or absorb energy
Grade 8 Science Worksheet
Circle the best answer, or write your answer on the line.
A reaction warms 100 g of water from 20 °C to 25 °C. Energy = mass × 4.18 J/(g·°C) × rise. How many joules did the water take in, Ari?
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?
Energy is kept in this reaction. How much thermal energy do the surroundings have after the reaction, Jun?
Energy is kept in Kira's reaction. How much thermal energy do the surroundings have after the reaction?
A cup of reacting powder keeps its total energy. How much thermal energy is in Luz's surroundings after the reaction?
Milo's card: a reaction needs a match flame to start, then keeps going by itself and the flask gets hot. Exothermic or endothermic?
- Endothermic, since it needed a flame to start
- Endothermic, since the flame gave it the energy it needed
- Exothermic: the flame only gets it started
- Neither, since a flame is not a kind of energy at all
Read this first
Energy for a burner-heated reaction (example data)
energy amount (kJ) absorbed by the reaction 30 released by the reaction 12 A reaction goes only while a burner heats it. Overall, is it exothermic or endothermic, Noah?
- Neither, since the two energy amounts are not equal
- Exothermic, since it released 12 kJ, which is real energy
- Exothermic, since a burner heating it makes things hot
- Endothermic: it absorbs 30 kJ and releases only 12 kJ
Pia's card: a reaction needs a burner to start, then keeps glowing and warming the table with the burner off. Which is it?
- Exothermic: the burner only started it
- Endothermic, since the burner supplied the energy
- Neither, since it glows
- Endothermic, since it needed a burner
The water cools after its peak. What is the best reason, Ren?
- The reaction turns endothermic and starts absorbing energy
- Energy is destroyed when the water is warmer than the room
- The reaction is done releasing, and the room takes energy
- Cold flows in from the cooler room into the water
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
- It released cold into the water, and the cold wore off
- Energy was destroyed in the dip, then made again later