1. Bell Work: Exo or Endo? Absorbs heat. Releases heat.
Internal temperature increases.
Surrounding temperature increases.
5. How is endothermic like breathing?
6. How is exothermic like shopping?

2. What do you think it’s all about?
Thermochemistry
What do you think it’s all about?

3. Thermochemistry is the study of energy/heat changes.
Energy can change in two ways:
In an endothermic process, energy is taken in and used to break bonds.
In an exothermic process, energy is released and used to form bonds.

4. Endothermic Processes: bond-breaking
The reactants have less energy than the products.
Energy must be absorbed from the surrounding environment in order to have enough energy to break the bonds in the reactants.
This leaves the surroundings feeling colder.

5. Endothermic Process ΔH Products Reactants Enthalpy
Ea = Activation Energy
Products
Enthalpy ΔH
Reactants
Reactants have less energy than products!

6. Exothermic Processes: bond-forming
The reactants have more energy than the products.
The extra energy must go somewhere so it is released as a product in order to form bonds to hold together the new products.
This extra energy is released to the surroundings making them warmer!

7. Exothermic Process ΔH Reactants Products Enthalpy
Ea = Activation Energy
Reactants ΔH
Enthalpy
Products
Reactants have more energy than products!

8. Phase changes occur because substances absorb and release heat
This means phase changes can be endothermic or exothermic

9. endothermic increase temperature decrease temperature exothermic solid
liquid
gas
decrease temperature
exothermic

10. **hint:
Try to think of phase changes in terms of water since water is familiar

11. fusion = melting
solid to liquid
endothermic

12. solidification = freezing
liquid to solid
exothermic

13. vaporization = evaporation
liquid to gas
endothermic

14. condensation
gas to liquid
exothermic

15. solid to gas (no liquid phase) endothermic
sublimation
solid to gas (no liquid phase)
endothermic

16. gas to solid (no liquid phase) exothermic
deposition
gas to solid (no liquid phase)
exothermic

17. evaporation/ condensation freezing/ fusion/ vaporization sublimation
solidification
fusion/
melting
deposition
energy

18. 2.
Deposition 3.
Condensation
Sublimation 4.
Vaporization 1. 5.
Fusion (melting) 6.
Solidification

19. Remember: temp = a measure of kinetic energy
increasing
increasing
fusion
vaporization
solidification
condensation
solid
liquid
gas
decreasing
decreasing