1. Calcium Chloride Ammonium Chloride
Demo
Calcium Chloride Ammonium Chloride
CaCl NH4Cl
feels _______ feels ______
Heat flows where?
into or out of ? into or out of ?
warmer
cooler

2. Law of Conservation of Energy:
In all chemical or physical processes, energy is neither created nor destroyed
(it must go somewhere)
Energy changes always involve
the system and the surroundings.
system:
the focus (reaction)
surroundings:
everything else around

3. NO exchange of matter or energy with surroundings
Open System:
exchange matter and energy with surroundings
(cup of hot coffee)
Closed System:
exchange only energy with surroundings
(cup of hot coffee with a lid)
Isolated System:
NO exchange of matter or energy with surroundings
(insulated cup of hot coffee)

4. CaCl2 NH4Cl
Exothermic:
system releases heat to surroundings
Endothermic:
system absorbs heat from surroundings
feels warmer
temp up
feels cooler
temp down

5. Total Energy Constant
(KE + PE)
Heat Energy (KE)
Chemical Energy (PE)

6. Potential Energy (PE) Diagram
(bonds broken)
(PE)
PEreac
Ea(+)
(weak bonds break)
H(–)
PEprod
(strong bonds form)
Stronger Bonds:
Lower PE (more needed to break)

7. (energy released when bonds form)
High PE
chemical bond
Low PE
(energy released when bonds form)
High PE
(energy absorbed when bonds break) + +

8. EXOthermic Potential Energy (PE) energy released “feels” warmer
(stronger)
(lower PE)
Rxn Progress

9. ENDOthermic Potential Energy (PE) energy absorbed “feels” cooler
(stronger)
(lower PE)
Rxn Progress

10. Describe the direction of heat flow as water melts.
from ___________
to ___________
ENDOthermic
surroundings
water

11. During freezing weather, farmers protect citrus crops by spraying them with water.
This is because...
as water cools, it releases a lot of heat (EXO–) to the oranges.

12. Quick Quiz!
How is an open system similar to a closed system? They both…
exchange matter in and out.
exchange energy in and out.
exchange matter and energy in and out.
are identical to an isolated system.

13. Quick Quiz.
2. The energy released when a piece of wood is burned has been stored in the wood as ___________.
sunlight energy
heat energy
calories
chemical potential energy

14. Quick Quiz.
3. Which of the following statements about heat is FALSE?
Heat is a measure of temperature.
Heat always flows from warmer objects to cooler objects.
Adding heat can increase the amount of energy of an object.
Heat flows because of a difference in temperature.

15. Quick Quiz.
4. Fill in the blanks:
In an endothermic process, the system ________ heat when heat is ________ its surroundings, so the surroundings _____________.
gains, absorbed from, cool down.
loses, released to, heat up.
gains, absorbed from, heat up.
loses, released to, cool down.