1. CHAPTER 10
ENERGY

2. 10.1 The Nature of Energy
The usual definition of energy: the ability to do work
Work is moving an object against an opposing force
Work = distance × opposing force [ w = d x f ]
SI unit of work or energy: the joule (J)

3. A joule
A joule is the mechanical equivalent of heat meaning the number of units of work which the unit of heat can perform.
Its value was found by James Prescott Joule in experiments that showed the mechanical energy which must be expended to raise the temperature of a unit weight of water by 1 degree F. was equivalent to 772 foot-pounds upon the Fahrenheit, thermometric scale, by reason of which it is often called Joule's equivalent, and represented by the symbol J.

4. Two basic types of energy
Potential Energy: energy of position
Examples
Boulder on a ledge
Cations and anions
Chemical bonds
Distance between particles
ie. H2O(s)  H2O(l)  H2O(g)
(gases have more PE than liquids and solids)
Tell how each of the examples above have potential energy.

5. Two basic types of energy
Kinetic Energy: energy of motion. It depends on the mass and velocity of the object. KE = ½ mv2
(where m = mass and
v = velocity)
Examples
Pool balls
Molecules
How do each of these have kinetic energy?

6. What happens to the energy when the ball hits the ground?

7. There are several forms of energy
Chemical Energy - stored energy that depends on the composition of the substance.
Food and gasoline
Nuclear Energy - energy involved in nuclear reactions.
Electrical Energy - the chemical reaction that occurs in the battery of a car produces electrical energy used to start the car and operate the headlights, radio, etc.

8. There are several forms of energy
Light Energy - plants use the radiant energy of sunlight to do the work of making carbon dioxide and water into sugar. This process of creating stored chemical energy is photosynthesis.
Mechanical energy – used to do mechanical work
Sound Energy
Thermal Energy – heat
Two things energy is NOT
Some sort of invisible fluid
Something which can be measured directly

9. Give another example of energy conversion
Energy can be converted from one form to another form which is more useful.
This occurs all around you on a daily basis. Example: Consider when electrical energy is converted into heat energy in a hair dryer.
Give another example of energy conversion

10. A fundamental law governs these energy conversions:

11. Law of Conservation of Energy
in any chemical or physical change, energy is neither created nor destroyed. (which other law does this remind you of?)
Energy may be converted from one form to another but it is always conserved. All the energy involved can be accounted for as work, stored energy, or heat.

12. 10.2 Temperature and Heat Thermal energy
Definition: energy due to chaotic molecular motions
Three factors affecting thermal energy
Temperature – Definition: a measure of the random motion of the components (atoms/molecules) of a substance
Higher temperature leads to higher thermal energy
Sample size
A cup of hot coffee has more energy than a teaspoon of coffee, all other things being equal.
Composition
E (solid) < E (liquid) < E (gas), all other things being equal

13. Heat
Anything that changes temperature, sample size and/or composition of an object can change its thermal energy
Heat Definition: transfer of thermal energy due to a temperature difference
Thermal energy isn't measurable, but heat is

14. Molecular logic time!!
Fill in the worksheet as we go through the animations together…

15. 10.3 Exothermic and Endothermic Processes
According to chemistry/physics, when studying reactions etc… the universe is divided into 2 parts:
The System: the part of the universe which you focus your attention.
The Surroundings: everything else in the universe.

16. Exothermic reaction Energy is lost to the surroundings as heat
What examples can you think of?
Think of it in terms of motion of particles

17. The energy changes accompanying the burning of a match

18. Endothermic reaction Energy is absorbed from the surroundings
What examples can you think of?
Consider this: If a chemical reaction gives off heat is it endothermic or exothermic?

19. Practice:
Are the following examples of endothermic reactions or exothermic?
Water freezing
Ice melting
Methane burning
Water boiling