Energy
Unit 6
What is Energy?
A burning
match
releases
energy.
Source:
ElektraVision/
PictureQuest
A Hindu firewalking ceremony in the Figi Islands. Could
you do this?
Source: Jack Fields/Photo Researchers, Inc.
Energy Notes
Energy
– Capacity to do work or produce heat
– Capacity to move or change matter
Energy Notes
Work
• Moving an object over a distance against
a resisting force
– Energy stored in the organized motion of
molecules
Examples
• A car traveling down the street
• A train moving down the tracks
• Pushing a book across the desk
Types of Energy
Potential
• Stored
– Energy of position (water wheel, book on
desk)
– Chemical energy (gas, food, batteries)
Kinetic
• Motion
– Mechanical energy (moving parts of
machines)
Radiant
• Thermal energy (Sun’s heat)
Sound
-Light
• Vibration of molecules
Energy Notes
Law of
Conservation
of Energy
• In any chemical or physical process,
energy is neither created nor
destroyed.
– Different forms of energy are equivalent.
• A particular amount of one type of energy can
be converted into an exactly amount of
another type of energy.
Energy Measurement
Joule
Energy Notes
Unit:
• Metric = joule (J)
• US = calorie (c)
– 1 calorie is the amount of heat needed to
raise 1 g of H2O by 1 °C
– 1000cal = 1Cal = 1 kilocalorie = food
Calories
Conversion (c
• 4.184 J = 1 cal
to J)
Energy Notes
Example
– A student uses 30 J of energy putting books
on the shelf in the classroom. How many
calories of energy did the student exert?
– A student eats an entire bag of plan
popcorn which contains 60.1 Calories. How
many Joules of energy is this?
– STOP Period 6
Brain Teaser
• Explain why the rug on your floor feels
warmer than the tile in the same room
• Convert 200 Calories to Joules
– 4.184 Joules = I calorie
– 1 Calorie = 1000 calories
Agenda
• Brain Teaser
• Collect Energy Lab Packet
• Energy Notes:
– Heat and Temperature
– Specific Heat
• Homework
– Temperature Conversion Worksheet
Heat and Temperature
Continue on this slide (P5)
Figure 3.12: Equal masses of hot water
and cold water separated by a thin metal
wall in an insulated box.
Is anything
going to
happen?
Figure 3.13: The H2O molecules in hot
water have much greater random
motions than the H2O molecules in cold
water.
Figure 3.14: The water samples now have
the same temperature (50°C) and have
the same random motions.
Heat and Temperature
Heat
• Energy transferred from one body to
another due to a temperature
difference.
– Energy stored in the random motion of
molecules
Examples
• Sunlight heating the earth
• Hot plate with beaker of water
Heat and Temperature
Exothermic
Endothermic
• System that releases energy into its
surroundings
• Release energy because a change has
occurred
• Combustion reactions
• System that takes energy in as heat
from the surroundings
• Need energy from outside source in
order for a change to occur
• Phase change – boil water
Endo vs. Exo
• Why are these types of reactions useful?
• What are some examples in your daily life?
Temperature
Temperature
• Measure of the average kinetic energy
of the particles in a sample of matter.
3 scales
• Fahrenheit (ºF)
• Celsius (ºC)
• Kelvin (K)
Temperature
Converting
between ºC
and K
• ºC = K – 273
• K = ºC + 273
Example
• Normal human body temperature is
37 ºC. What is your temperature in K?
• Surgical instruments must be sterilized
at 170 ºC. What is this in K?
Practice
Temperature
Converting
between ºC
and ºF
• ºC = 5/9(ºF – 32)
• ºF = 9/5 ºC + 32
Example
• It is 100 ºF outside. What temperature
is this in ºC?
Practice
• The boiling point of methanol is
164 ºC. What is the boiling point is ºF?
Heat versus Temperature
(continue on this slide P2,4)
• Heat
– Energy that transfers from one object to another
because of a temperature difference between
them.
• Temperature
– A measure of the average kinetic energy of the
particles in a sample of matter
Refer to Temperature Worksheet
Brain Teaser (1/17)
• Convert 200 Calories to Joules
Agenda
•
•
•
•
Brain Teaser
Notes: Specific Heat and Calorimetry
Post Lab Activity: Energy Lab
Homework
– Practice Problems 1-6
Specific Heat and Calorimetry
Specific Heat and Calorimetry
• Specific Heat
• What this means
• amount of heat that can be
absorbed by 1 gram of material
when its temperature increases
by 1oC; unit = J/g oC
• What bench would you rather
sit on, wood or iron, in the
summer in AZ? Why?
Specific Heat
• Which holds more heat when
exposed to 120oF sunlight -- a
wood or an iron bench (both at
the same temperature)?
• Compare the specific heat
capacities.
Iron 0.448 J/goC, wood 1.76 J/goC
• The wood bench holds onto
more heat so it does not transfer
as much to you.
Specific Heat and Calorimetry
• Calorimetry
• Measurement of the amount of
energy released or absorbed
during a chemical reaction
• Calorimeter
• Device used to measure the
transfer of energy to water
Complex Calorimeter
Simple Calorimeter
Test Tube
Thermometer
Stirring Rod
Water
Reaction
Sealed
Container
Energy
Endo vs. Exo
• Endothermic- reaction
absorbs energy temperature
of the surrounding water goes
down
• Exothermic - reaction gives
off energy temperature of the
surrounding water goes up
How does the Heat Flow and How do
you Know?
Three factors determine the amount of
energy (Q) transferred to or from the water.
Q= mCpT
1. Mass of the water in the
calorimeter (units = grams)
2. Specific Heat of water
1cal
4.184 J
or
g  C
g  C
3. Change in the water’s
temperature. T = Tfinal- Tinitial
(units = ºC)
Q= mCpT
• Example 1
specific heat 1cal
4.184 J
or
for water
g  C
g  C
• How many calories must be added
to 5000 g of water to change it
temperature from 20 to 30ºC?
• Practice 1
• How many calories are needed to
increase the temperature of 150.0
grams of water from 40.0 to
65.0ºC?
Q= mCpT
• Example 2
• Practice 2
specific heat 1cal
4.184 J
or
for water
g  C
g  C
• A 2.0 x104 grams sample of water
has its temperature raised by 3ºC.
How many Joules of energy was
produced?
• What is the number of Joules
needed to increase the
temperature of 50.0 grams of
water 15.0ºC?
Q= mCpT
• Example 3
specific heat 1cal
4.184 J
or
for water
g  C
g  C
• If 500.0 g of water at 25ºC loses
2500 calories, what will be the final
temperature?
• Practice 3
• What is the final temperature after
80.0 calories is absorbed by 10.0
grams of water at 25ºC?
Q= mCpT
• Example 4
• Practice 4
specific heat 1cal
4.184 J
or
for water
g  C
g  C
• What temperature change,in
Celsius, is produced when 6.0 x102
grams of water gives off 9.60
kilocalories?
• What is the change in temperature
when 640 calories is given off by
40 grams of water?
Q= mCpT
• Example 5
• Practice 5
• What is the specific heat of lead if
a 30.0 g piece of lead undergoes a
250ºC change while absorbing
229.5 calories?
• What is the specific heat of an
unknown substance if the addition
of 950 J of heat energy caused a 20
gram sample to warm from 18ºC to
42ºC?
Q= mCpT
• Example 6
• Practice 6
• A quantity of water is heated from
25.0ºC to 36.4ºC by absorbing 325
calories. What is the mass of the
water?
• What is the mass of a piece of
copper that undergoes a 25.0ºC
temperature change when it
absorbs 755 J of energy? Copper
has a specific of
0.387 J
g  C
PreLab: Energy Content in Foods
Time to get your lab books ready for Lab!
Use the lab handout to help you complete all of the
following according to the grading rubric.
1. Title
2. Purpose
3. Background information
4. Materials
5. Procedure and safety
6. Set up data table
Class Results
Group
1
2
3
4
5
6
7
8
Ave.
Peanut
J/g
Potato Chip
J/g
Popcorn
J/g
Marshmallow
J/g
Class Results 6th Period
Group
Peanut
J/g
Cashew
J/g
Popcorn
J/g
Marshmallow
J/g
1
2
3
4
5
6
7
8
Ave. 16,500
11,300
687
2830
Review Lab- Energy Content in Foods
5. Food energy is expressed in Calories. 4.184 kJ in
1.000 Calories. Based on the class average for
peanuts, calculate the number of calories in a 50.0
g package.
6. Product labels. Determine a serving size and use
the class average to calculate the number of
calories present in a single serving. Compare your
results to the nutritional information.
Review Lab- Energy Content in Foods
1. What are 2 possible sources of error? What
could be done to reduce these errors?
2. How does calorimetry make use of the law
of conservation of energy?
3. What generalization can you make about the
relative energy content of fats and
carbohydrates?
Product Labels
16 oz = 453.59 g
Peanuts – 1 oz, 180 Calories
Cashews – 1 oz, 160 Calories
Popcorn – 1 cup popped, 25 Calories (7g~1 cup)
Marshmallow – 30 g, 100 Calories