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
40 g CaCl2 (100 mL Water) AND 30 g NH4Cl (100 mL)

2. Law of Conservation of Energy:
In all chemical or physical processes, energy is neither created nor destroyed
(it must go somewhere)
system:
the chemical reactants and products in the reaction
surroundings:
everything else around (hands, thermometer, etc.)

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

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

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

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

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

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

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

10. 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.

11. Quick Quiz!
1. 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

12. Quick Quiz.
2. 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.

13. Quick Quiz.
3. 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.