Breaking a bond takes energy. Forming one releases it.
- The idea
- Predict
- See it
- Why
- Check
The idea
“Bonds store energy, so breaking a bond releases the energy inside it.”
You've heard that food stores energy in its bonds and ATP has high-energy bonds. So a bond sounds like a battery that empties when it snaps.
The short version
The mistake: Bonds store energy, so breaking a bond releases the energy inside it.
What's actually true: Breaking any bond takes energy. Forming one releases it. A reaction gives off energy overall when its new bonds are more stable.
- Pulling bonded atoms or molecules apart always takes energy. That goes for hydrogen bonds and for the covalent bonds in ATP.
- Energy comes out when bonds form, often as heat, because the atoms settle at lower potential energy.
- A reaction is exergonic when forming its new bonds gives out more energy than breaking the old ones took in.
- ATP hydrolysis is one. Its products, ADP and phosphate, are more stable than ATP and water.
On the exam: Breaking bonds costs energy. Forming bonds gives it back.