# Mon, February 25

```Do Now
Grab a notecard and select TWO subtopics
from the study guide that you are not confident
in. On one side, write everything you know about
one topic. On the other side, write everything
you know about the other topic.
Get any make-up work from last week now!
Today’s Agenda
5 min
•Do Now
5 min
•Important Dates
40 min
•Unit Exam Review
10 min
•Practice Test
Today’s Agenda
5 min
•Do Now
5 min
•Important Dates
40 min
•Unit Exam Review
10 min
•Practice Test
Important Dates and Reminders


Unit Exam on Thursday
Practice Test Due Wednesday
 Worth

Tutoring This Week
 Today


and Wednesday from 3:30-4:30 PM
 Check

double points on homework!
TeacherEase for what’s missing
Monthly News Project Due Thursday
Monthly Raffle This Thursday &amp; Prizes Friday
Today’s Agenda
5 min
•Do Now
5 min
•Important Dates
40 min
•Unit Exam Review
10 min
•Practice Test
Unit Exam Topics







Temperature
Heat
Specific Heat
Quantity of Heat
Types of Heat Transfer
1st Law of Thermodynamics
2nd Law of Thermodynamics
What is Temperature?


Temperature is simply the reading on a
thermometer.
Other good but not complete definitions:
 The
degree of hotness or coldness of a body or
environment.
 A measure of the average kinetic energy of the
particles in a sample of matter, expressed in terms of
units or degrees designated on a standard scale.
Temperature Scales
Celsius Scale

Most widely accepted
temperature scale
used all over the
world.
Farenheit Scale

 FP:
0 &deg;C
 BP: 100 &deg;C

&deg;C = (&deg;F - 32&deg;)/1.8
The US likes to do
things its own way so
uses this temperature
scale
 FP:
32 &deg;F
 BP: 212 &deg;F

&deg;F= 1.8•&deg;C + 32&deg;
Kelvin Temperature Scale

Most widely used scale for scientists
K = &deg;C + 273.15
Practice Problems

Convert the following:
 38
&deg;C to &deg;F
 92 &deg;F to &deg;C
 65 &deg;C to K
 70 &deg;F to K
Practice Problems

Convert the following:
 38
F
 92
C
 65
K
 70
K
&deg;C to &deg;F
= (1.8*38) + 32 = 100.4 &deg;F
&deg;F to &deg;C
= (92-32)/1.8 = 33.3 &deg;C
&deg;C to K
= 65 + 273 = 338 K
&deg;F to K
= [(70-32)/1.8] + 273 = 294.1 K
What does temperature measure?


Temperature is a measure of the average kinetic
energy of the particles within a sample of matter.
When the temperature of an object increases,
the particles that compose the object begin to
move faster.
 They
either vibrate more rapidly, rotate with greater
frequency or move through space with a greater
speed.
 A thermometer is kind of like a speedometer!
Heat is the flow of energy
Check for Understanding
What would be the direction of heat transfer
when putting ice to a burn on your skin?
Create your own example of a heat transfer
that would occur in real life between objects that
have a temperature difference.
Quantity of Heat
The unit of heat is defined as the energy
necessary to produce some standard change.
The most commonly used unit for heat is the
calorie.
So what does heat do?

Heat changes the temperature of objects.
 If
heat is transferred FROM an object to the
surroundings, then the object can cool down and the
surroundings can warm up.
 When heat is transferred TO an object by its
surroundings, then the object can warm up and the
surroundings can cool down.
Temperature vs. Heat
Temperature

Measure of the
hotness/coldness and
the kinetic energy
Heat

Transfer of energy
from hot object to cold
object
Specific Heat Demo Recap
We are going to recap the demo we did using a
balloon filled with water and a balloon filled
with air. Let’s discuss what happened and why.
Specific Heat


Different substances have different abilities to store
energy.
The specific heat of a substance is defined as the
quantity of heat required to change the
temperature of a unit of mass (like a gram or
kilogram) of the substance by 1 degree.
 Symbol:
c
 Unit: J/g/&deg;C.
Check for Understanding

Water has a specific heat capacity of 4.18 J/g/&deg;C.
Vegetable oil has a specific heat capacity of of
0.67 J/g/&deg;C.
 Which
one has a greater specific heat capacity?
 What does that tell you about water vs. oil?
Check for Understanding

Water has a specific heat capacity of 4.18 J/g/&deg;C.
Vegetable oil has a specific heat capacity of of
0.67 J/g/&deg;C.
 Which
one has a greater specific heat capacity?
 Water
 What
does that tell you about water vs. oil?
Check for Understanding

Water has a specific heat capacity of 4.18 J/g/&deg;C.
Vegetable oil has a specific heat capacity of of
0.67 J/g/&deg;C.
 Which
one has a greater specific heat capacity?
 Water
 What
 It
does that tell you about water vs. oil?
is harder to change the temperature of water than
vegetable oil. Water can store more energy.
Check for Understanding

Water has an unusually high specific heat capacity.
Which one of the following statements can we say
knowing that fact?
A.
B.
C.
Compared to other substances, hot water causes bad
burns because it is a good conductor of heat
Compared to other substances, water will quickly
warm up to high temperatures when heated.
Compared to other substances, it takes much more
heat for a sample of water to change its temperature
by a small amount.
Check for Understanding

Water has an unusually high specific heat capacity.
Which one of the following statements can we say
knowing that fact?
A.
B.
C.
Compared to other substances, hot water causes bad
burns because it is a good conductor of heat
Compared to other substances, water will quickly
warm up to high temperatures when heated.
Compared to other substances, it takes much more
heat for a sample of water to change its
temperature by a small amount.
Quantity of Heat

We can find the amount of thermal energy gained
or lost by any substance by using the mass of the
substance, its specific heat capacity and the
temperature change.
Q = mcΔT
Positive Q: object gained energy
Negative Q: object lost energy
Warm Up Problem

A 80-gram sample of water is heated from 19&deg;C to
28&deg;C. Determine the heat gained by water. The
specific heat capacity of water is 4.18 J/g/&deg;C.
Warm Up Problem

A 80-gram sample of water is heated from 19&deg;C to
28&deg;C. Determine the heat gained by water. The
specific heat capacity of water is 4.18 J/g/&deg;C.
Q
= (80 g)(4.18 J/g/&deg;C)(28 &deg;C – 19 &deg;C)
 Q = 3009.6 J
Teach-A-Friend Problem

A sample of water loses 125 Joules of heat when it
cools from 95&deg;C to 60&deg;C. What is the mass of the
water sample? The specific heat capacity of water
is 4.18 J/g/&deg;C.
Teach-A-Friend Problem

A sample of water loses 125 Joules of heat when it
cools from 95&deg;C to 60&deg;C. What is the mass of the
water sample? The specific heat capacity of water
is 4.18 J/g/&deg;C.
 -125
J = m(4.18 J/g/&deg;C)(60 &deg;C – 95 &deg;C)
 -125 J = m(-146.3 J/g)
 m = 0.85 g
Class Team Problem

A piece of metal with a specific heat of 0.520
J/g/C and an initial temperature of 95&deg;C is placed
in a calorimeter that holds 40 g of water. The
initial temp of the water is 15&deg;C and the final temp
of the system is 30&deg;C. What is the mass of the
metal?
Class Team Problem

A piece of metal with a specific heat of 0.520
J/g/C and an initial temperature of 95&deg;C is placed
in a calorimeter that holds 40 g of water. The
initial temp of the water is 15&deg;C and the final temp
of the system is 30&deg;C. What is the mass of the
metal?
 QW =
(40 g)(4.18 J/g/&deg;C)(30 &deg;C – 15 &deg;C)
 QW = 2508 J  QM = -2508 J
 -2508
J = m(0.520 J/g/&deg;C)(30 &deg;C – 95 &deg;C)
 -2508 J = m(-33.8 J/g)
 m = 74.2 g
Types of Heat Transfer
•
•
•
Conduction
Convection
Conduction




Conduction – Transfer of heat through
matter by the direct contact of particles.
Since molecules are always moving, whenever
there is direct contact between two things, the
molecules from one object will collide with the
molecules of the other object.
Happens mostly in solids.
What are examples of situations where
conduction occurs?
Convection




One way that liquids and gases differ from solids
is that they can flow. (What does flow mean?) This
makes them fluids.
Convection – heat transfer in a fluid by
movement of heated particles.
Particles actually move from one place to another
What are examples of situations where convection
occurs?



Radiation is the transfer of energy by
electromagnetic waves.
NOT require any matter. (It can happen in empty
space!)
What are examples of situations where radiation
occurs?
First Law of Thermodynamics
The First Law of Thermodynamics basically states
that in a closed system, energy can neither be
created nor destroyed, only transformed or
transferred. There is an energy balance in the
universe.
Another Look at Q
Q = DE – W
Q = (EF– EI) -W
Q = heat added TO THE SYSTEM
DE = D in internal energy
W = Work done ON THE SYSTEM
If the system does work, W is NEGATIVE
Practice Problem

An object has an initial internal energy of 50 J. The
internal energy increases to 75 J when 20 J of work
is done. What is the amount of energy in the form
of heat that was gained by the system during this?
Practice Problem

An object has an initial internal energy of 50 J. The
internal energy increases to 75 J when 20 J of work
is done. What is the amount of energy in the form
of heat that was gained by the system during this?
 Q = DE – W
Q
= (75 J – 50 J) – 20 J
Q=5J
Second Law of Thermodynamics
The entropy of the universe increases in all natural
processes and reactions.
Entropy is the measure of a system’s disorder.
Calculating Entropy

When a body absorbs
an amount of heat Q
from a reservoir at
temperature T, the
body gains and the
surroundings lose an
amount of entropy
 Positive
S: Entropy
Increased
 Negative S: Entropy
Decreased
Practice Problem

A system starts out at 55 C. It gains 20 J of heat
causing its temperature to increase to 60 C. What
was the increase in entropy?
Practice Problem

A system starts out at 55 C. It gains 20 J of heat
causing its temperature to increase to 60 C. What
was the increase in entropy?
 ΔS
= Q/ΔT
 ΔS
= 20 J/(60 &deg;C – 55 &deg;C)
 ΔS = 4 J/&deg;C
Big Questions
Any questions from the material that we have
reviewed that should be addressed whole
group?
Today’s Agenda
5 min
•Do Now
5 min
•Important Dates
40 min
•Unit Exam Review
10 min
•Practice Test
Practice Test
You have the next 10-15 minutes to work
independently on your practice test. You should
only be using notes as a last resort and when
using notes, only use them as a GUIDE.
Remember that when you take the exam, you will
have no notes so you should practice for the
exam in the same way.
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