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