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An Introduction to Energy
Unit 2, Presentation 1
What is Energy?
Energy is defined as the ability to do work
Work is any force applied over a distance
Six Different Types of Energy
Type of Energy Field of StudyHeat Thermodynamics
Sound Acoustics
Light (Electromagnetic Radiation)
Optics
Chemical Chemistry
Electrical Electromagnetism
Mechanical(Kinetic & Potential)
Mechanics
*Nuclear Energy is a special case*
SI Unit for Energy
Energy is measured in Joules (J) Named in honor of James Joule (British)
Can also be measured in Calories (cal) One calorie = amount of energy needed to
warm one gram of water one Kelvin. One calorie ~ 4.20 Joules
2
2
s
mkgJ
Conservation of Energy & Mass
Energy is neither created nor destroyed in a chemical reaction
Mass is neither created nor destroyed in a chemical reaction
Types of Chemical Reactions
Exothermic: A chemical reaction that releases heat energy. Expressed as the following:
Reactants Products + Energy
Endothermic: A chemical reaction that absorbs heat energy. Endothermic reactions require heat energy to be completed. Expressed as the following:
Reactants + Energy Products
Heat Energy and Temperature
Temperature is a measure of heat energy Three measures of temperature:
Degrees Fahrenheit Degrees Celsius Kelvin (Absolute Temperature)
Comparison of Three Temperature Scales
Fahrenheit Scale
Celsius Scale
Kelvin Scale
Boiling Point of Water
212 100 373
Body Temperature
98.6 37 310
Freezing Point of Water
32 0 273
Absolute Zero
-460 -273 0
Making a Celsius Thermometer
Converting to Kelvin
The Absolute Temperature (Kelvin) scale is most often used
K = °C + 273.16
Hence, 0.0000°C = 273.16K
Calorimetry
Calorimetry: The measurement of the amount of heat released or absorbed during a chemical reaction.
TmcQ
of TTT
KetemperaturT
change
kgmassm
joulesheatQ
)(
)(
)(
Calorimetry Example
A 2000. gram mass of water has its temperature raised 3.0°C while an exothermic chemical reaction is taking place. How much heat is transferred to the water by the heat of the reaction (the specific heat of water is 4184 J/kg K)?
CT
Kkg
Jc
kggm
Q
w
0.3
4184
000.2.2000
?
JQ
JTmcQ4105.2
250000.34184000.2
Another Calorimetry Example
A 1000. gram mass of water whose temperature was 50.0°C lost 33 600 J of heat over a 5-minute period. What was the temperature of the water at the end of the 5-minute period? Use the same specific heat of water as the previous example.
KCT
T
Kkg
Jc
kggm
JQ
o
f
w
3230.50
?
4184
000.1.1000
33600
CT
TTmc
Q
TTmcTmcQ
f
fo
of
0.430.504184000.1
33600
)(
Kinetic Theory of Heat & Temperature
Heat energy, measured by temperature, is directly proportional to the average kinetic energy of the molecules in the substance. As temperature increases, so does the
average speed of the molecules in the substance
As temperature decreases, so does the average speed of the molecules in the substance.
More Kinetic TheoryMore Kinetic TheoryMore Kinetic TheoryMore Kinetic Theory
Matter consists of atoms Matter consists of atoms and molecules in and molecules in motion.motion.
v
Solid Liquid Gas
Low Energy Moderate Energy High Energy
Slow Molecules Fast Molecules
Slow vibratory motions
Still mostly vibrations, but slightly faster