Reactions that release or absorb energy
Grade 8 Science Worksheet - Building Confidence
Circle the best answer, or write your answer on the line.
A reaction in a teacher's cup changes the water from 21 °C to 29 °C. Change = end − start. What is the temperature change, Ari?
Bo reads that a reaction changes its water from 24 °C to 19 °C. Change = end − start. What is the temperature change? (A cooling is negative.)
A cold pack's mix takes the water from 25 °C down to 12 °C. Change = end − start. What is the temperature change, Esme? (A cooling is negative.)
The water in Jun's cup changes by −5 °C during a reaction. What did the reaction do?
- Nothing, since a negative number means no change
- Released cold into the water
- Absorbed energy from the water: it was endothermic
- Released energy into the water, since the number is a change
The water in Kira's cup changes by +12 °C during a reaction. What did the reaction do?
- Absorbed energy from the water, since the water gained heat
- Released energy to the water: it was exothermic
- Made energy out of nothing for the water
- Nothing, since a positive number means no change
A reaction makes Luz's beaker feel cold. What is happening to the energy?
- The reaction gives out cold, which flows into the beaker
- The reaction gives energy to the beaker and the hand
- Glass feels cold whatever the reaction does
- The reaction takes energy from the beaker and the hand
Which statement fits the energy bars for Milo's reaction?
- Endothermic: the thermal bar grew, so it absorbed energy
- Exothermic: 30 kJ of chemical energy became thermal energy
- Neither: the chemical bar changed, so energy was lost
- Exothermic: 60 kJ of new energy was made
The thermal bar grows in this chart. Where did that extra energy come from, Pia?
- The reaction made new energy while it ran
- From the walls of the cup, which lost energy
- From the cold surroundings, which gave their energy away
- From the chemical store, which fell by 30 kJ
On a snowy day, iron in Ren's hand warmer reacts with air and the packet heats up. What does the reaction do?
- Stores sunlight and gives it off slowly
- Releases energy as heat that warms the hands
- Absorbs heat from the hands to make the packet hot
- Makes cold leave the hands
Tala squeezes an instant cold pack, and it turns cold. What is happening inside the pack?
- The reaction releases energy that makes the pack cold
- Ice forms in the pack from the squeezing
- The reaction absorbs energy from around it
- The reaction makes cold and gives it to the arm