1. Energy
Chapter 16

2. Energy: Ability to do Work
Potential Energy = Energy of position
Also called STORED ENERGY
Kinetic Energy = Energy of motion
Radiant Energy = Electromagnetic
Ex: Sunlight

3. Types of Energy
(Not a complete list!)

4. Units of Energy SI system - unit of energy is JOULE (J)
1 Joule = amount energy required to lift golf ball 1 meter

5. Other Energy Units:
calorie, Calorie, BTU’s
1 calorie = 4.18 Joules
1 Calorie = 1000 calories = 1 kilocalorie

6. Kinetic Energy KE = ½ x Mass x Velocity2 = ½ mV2 So KE depends on:
how heavy
how fast

7. Potential Energy Kleenex Box Spring Rubberband Popper
Anything can have
PE = energy of position
= stored energy
PE can be converted to KE

8. Magnets
2 magnets:
PE depends on relative position

9. Electromagnetic Radiation
Sunlight – Visible radiation
Ultraviolet radiation
Infrared radiation
Gamma rays
X-rays
Microwaves
Radiowaves
Applet spectrum

10. Energy in Chemistry Chemical energy = energy stored in bonds
Heat = form energy that flows from warmer object to cooler object
(Macroscopic)

11. Heat Energy
Heat: energy associated with motion of atoms & molecules in matter
(Microscopic)
Symbol for heat energy = Q or q

12. Heat Energy
Heat depends on amount of substance present
measure changes in heat

13. Temperature measure of average KE of particles of substance
Swimming Pool vs. Mug
Temperature is NOT energy
Temperature does not depend on amount of substance; energy does

14. Law of Conservation of Energy
Energy is neither created nor destroyed in ordinary chemical or physical change
Energy before = Energy after
Energy can be converted from one form to another
- potential to kinetic radiant to electric
- electric to heat chemical to kinetic
- chemical to electrical

15. All physical and chemical changes are accompanied by energy changes
chemistry of energy changes =
Thermochemistry!

16. Energy Transfer Measure changes in heat
amount energy transferred from one
substance to another
measure energy lost somewhere or
energy gained somewhere else
Cannot measure absolute heat content

17. Energy of Universe is conserved
Energy can move between system
and environment
Environment
System
Energy
Environment

18. Exothermic Change System releases heat to environment
EXO - energy leaves system (exits)

19. EXO - energy leaves system (exits)
Environment
System
Energy
Temperature of environment 
Temperature of system 

20. Exothermic Change
System has net loss in energy!
Environment has net gain in energy!
Energy lost = Energy gained

21. Endothermic Change System absorbs heat from environment
Endo - Energy enters system

22. Endo - Energy enters system (entrance)
Environment
System
Energy
Temperature of environment 
Temperature of system 

23. Endothermic Change
System has net gain in energy!
Environment has net loss in energy!
Energy lost = Energy gained

24. Heat Flow Heat flows from hotter object to cooler object
Cold pack on leg:
Heat flows from leg to cold pack!
Leg cools down; cold pack warms up

25. Quantity of heat transferred
Quantity (amount) of heat transferred depends on
Temperature change
Mass of substance
Specific Heat of substance

26. Calculating Heat Transferred
Q = mCT
Q = amount of heat transferred
m = mass of substance
C = specific heat capacity of the substance.
T = temperature change = Tfinal – Tinitial

27. Specific Heat Amount heat energy required to
raise temp of 1 gram of substance by 1 oC
Symbol = c
Specific heat = a physical constant
Different for each pure substance

28. Calorimeter

29. Another example
source

30. Calorimetry Changes in heat energy are measured by calorimetry
The “universe” is contained in a styrofoam cup
The “enviroment” is the water****
The “system” is whatever is put in water

31. Calorimetry Energy lost = Energy gained Difficult to monitor “system”
Easy to monitor “environment (water)”
Energy lost/gained by environment =
Energy gained/lost by system

32. Calorimetry
10 grams of NaOH is dissolved in 100 g of water & the temperature of the water increases from 22C to 30C
was the dissolving process endothermic or exothermic
how do you know?
Exothermic – the temperature of the environment increased

33. Dissolving What’s happening when the NaOH dissolves? Add H2O
molecules close together,
not interacting
molecules pulled apart & interacting with H2O

34. Calorimetry Q = mCT Q = energy (joules) M = mass (grams)
Calculate energy released by NaOH in previous problem as it dissolved in water
Energy lost by NaOH = Energy gained by water Easier to calculate from H2O perspective
Q = mCT
Q = energy (joules)
M = mass (grams)
C = specific heat capacity (Table B)
T = temperature change = Tf - Ti

35. Calorimetry & Q = mCT
temperature of water increased from 22C to 30C
30C -22C = 8C = T
What mass to use? Well, temp change was for water, so use mass of water m = 100 g
Same goes for specific heat capacity; calculate heat absorbed by water
cH20 = 4.18J/g C

36. Q = mCT
Q = (100 g)(4.18 J/g)(8C)
Q = 3344 Joules

37. Stability and Energy If energy is high, stability is low
If energy is low, stability is high