Physical Science / Unit 5: Chemical Reactions
5.5 Energy in Reactions
Notes
Breaking bonds takes energy; forming bonds releases energy.
- Exothermic reactions release energy (heat or light) to the surroundings: burning, cellular respiration. The surroundings get warmer.
- Endothermic reactions absorb energy: photosynthesis, cooking an egg, cold packs. The surroundings get cooler.
- Activation energy is the minimum energy needed to start a reaction. A match provides it to start combustion.
- Energy is conserved: it changes form but is not created or destroyed.
Practice
A chemical cold pack gets cold when activated. This reaction is:
It absorbs heat from its surroundings.
What is activation energy?
Even exothermic reactions need a push to get started.
Wood burning in a campfire is an example of:
Burning releases heat and light.
Ready for more? Take the Unit 5 test.