1. Unit 4 Thermodynamics- Lecture 2:
PS 1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy. a. Students know how to describe temperature and heat flow in terms of the motion of molecules (or atoms). b. Students know chemical processes can either release (exothermic) or absorb (endothermic) thermal energy.

2. Unit 4 Lecture 2: Temperature and Heat

3. Unit 4 Lecture 2:
d. They are all sitting at the same ambient temperature so they
will have the same average kinetic energy.

4. Unit 4 Lecture 2: Energy Initial model
Come up with a model to show what would happen if you take two equal amounts of water, one at 00C and one at 1000C and mix together.
Remember models both show what happens and explain WHY!
Show what happens at the macroscopic (visual) and particle levels

5. Heat: A form of energy that flows from a warmer object to a cooler object.
The warmer object loses heat and becomes colder (temperature lowers)
The colder object absorbs heat and become warmer (temperature rises)

6. Measuring Heat energy:
Three major energy units:
Joule (J), calorie (cal), Food Calorie (Cal)
1 calorie = joules
Food Calories are equivalent to kilocalories (Kcal)
1 Calorie = 1 Kcal= 1000 calories

7. Example #1 Convert 60.1 cal to joules19

8. Example #1 Convert 60.1 cal to joules
1 cal = joules
60.1 cal x J =
1 cal
= 251 J 19

9. Example #2 A reaction released 8650 joules, how many Food Calories of energy are released?19

10. Example #2 A reaction released 8650 joules, how many Food Calories of energy are released?
1 cal = joules, 1000 cal = 1 Cal
8650 J x _1 cal x 1 Cal =
4.184 J cal
= 2.07 Calories 19

11. Temperature: A measure of the average kinetic energy of the particles in a sample of matter.
- We measure in K or 0C

12. An example of Heat transfer between two boxes.
Watch the heat flow PowerPoint and come up with a model of what happened to the boxes when they came in contact. Remember a model shows what happens and why. This should include information at the macroscopic and particle levels.
Heat Flow PowerPoint

13. PhET Energy Forms and Changes
Do the PhET activity.

14. Virtually every reaction either releases or absorbs heat.
Thermochemistry: Study of heat changes in reactions
Law of conservation of energy: Energy is neither created nor destroyed within the universe
The universe consists of the system and the surroundings.
System: the reacting particles
Surroundings: everything else including all non-reacting particles.

15. Chemical Energy: Is the energy within bonds in chemical compounds (form of potential energy)
When bonds break they absorb energy (endothermic)
When bonds form they release energy (exothermic)

16. Exothermic and Endothermic Reactions:
All Chemical reactions require breaking bonds which absorbs energy and making bonds which releases energy.
The overall change in energy results in a reaction that is either Exothermic or Endothermic.
- always from the view of the system

17. Potential Energy of Reactants vs. Products

18. Products have less potential energy so Exothermic

19. Examples…. *It feels HOT because surroundings heat up
Exothermic:A process that has an overall release of energy
*It feels HOT because surroundings heat up
Reactants  Products + ENERGY
Examples….
O2 + H2  H2O + energy
SnCl2(s) + Cl2 (g)  SnCl4 (s) + 186KJ
Burning sugar
Rusting iron
Mixing acid and water
Water condensing

20. Examples…. *It feels COLD because surroundings cool down
Endothermic: A process that has an overall absorption of energy
*It feels COLD because surroundings cool down
Reactants + ENERGY  Products
Examples….
Sunlight + CO2 + H2O  C6H12O6 + O2
N2(g) + O2 (g) + 180KJ  2NO (g)
Producing sugar by photosynthesis
Forming a cation from a gaseous atom
Baking bread
evaporation