Download Thermodynamics

Thermodynamics
"Thermodynamics is a funny subject. The first time you go through
it, you don't understand it at all. The second time you go through it,
you think you understand it, except for one or two small points. The
third time you go through it, you know you don't understand it, but
by then you are so used to it, it doesn't bother you any more."
Arnold Sommerfield
What is temperature?
http://www.schooltube.com/video/2718a7a7fad74d4a839b/
Eureka!%20-%20Measuring%20Temperature
http://highschoolenergy.acs.org/content/hsef/en/what-is-energy/thermometers.html
Start with some definitions
Start with some definitions
http://www.schooltube.com/video/5574f4544a2d3b76d0ed/
Eureka!%20Episode%2021%20-%20Temperature%20vs.
Heat vs. Temperature
%20Heat
Which has a higher temperature, the bonfire
or the match?
Which has more heat, the bonfire or the
match?
http://www.flickr.com/photos/16224308@N05/3662777580/
http://www.patheos.com/blogs/slacktivist/the-bonfire/
Which has a higher temperature, an ice cube
or an iceberg?
Which has more heat, an ice cube or an
iceberg?
http://www.flickriver.com/photos/tags/!"#$/interesting/
http://wordlesstech.com/2012/12/28/iceberg-in-pleneau-bay/
Energy
Is the capacity to do work or cause change.
Work
is done when an object is moved in the direction in
Work
done when
an object is moved in the direction in which a force is
which
aisforce
is applied.
form of energy based on moving an object over a
distance
Other Forms of Energy
chemical, electrical, mechanical light (radiant)
sound, magnetic
Potential & Kinetic Energy
Potential Energy
Stored energy that an object has by virtue of its
position or composition.
Kinetic Energy
Energy of motion or
Energy of a reaction
http://www1.curriculum.edu.au/sciencepd/readings/ener.htm
1. The movement of water from the ground through the trunk to the upper limbs
of a tree is an important biological process.
A. What part of the system if any, undergoes a change in potential energy?
B. Is work done in the process?
The water changes position --against the force of
gravity so it’s potential energy has changed.
Work is movement of a mass over a distance
against an opposing force.
The tree does work in lifting the
water to its upper limbs
http://www.aperfectworld.org/clipart/plants/tree09.gif
2.
Which of the following involves the larger change in potential
energy?
A. a 50 kg object is dropped to the ground from a height of
8m?
B. a 20 kg object is lifted from the ground to a height of 20 m?
PE = mgh
A.
Magnitude of PE = (50 kg)(9.8 m/s2)(8m)
= 3920 J ---> 4000 J
B. Magnitude of PE = (20 kg)(9.8 m/s2)(20m)
= 3920 J-----> 4000J
Difference is the direction (sign) of the
change.
in A the sign is negative
in B the sign is positive
http://www.sign-maker.net/images/safety-sign-images/7715-falling-objects.jpg
3. A bowler lifts a 5.4 kg (12 lb)bowling ball from ground level to a height of
1.6 m (5.2 feet) and then drops the ball back to the ground.
A. What happens to the potential energy of the bowling ball as it is raised from the ground?
The ball is raised to a greater height above the
ground--therefore its PE
INCREASES
http://www.freefever.com/freeclipart/clipart/bowling.gif
3. A bowler lifts a 5.4 kg (12 lb)bowling ball from ground level to
a
height of 1.6 m (5.2 feet) and then drops the ball back to the
ground.
B. What quantity of work in J is used to raise the ball?
WORK = FORCE X DISTANCE
FORCE = MASS X ACCELERATION
WORK = MASS X ACCELERATION X DISTANCE
W = 5.4 kg x 1.6 m x 9.8 m/s2
W = 84.672 J
W = 85 J
3. A bowler lifts a 5.4 kg (12 lb)bowling ball from ground level to a
height of 1.6 m (5.2 feet) and then drops the ball back to the
ground.
C. After the ball is dropped, it gains kinetic energy. If we
assume that all of the work in part B is converted to KE
at the point of impact with the ground, what is the speed
of the ball at the point of impact?
KE= 1/2 mv2
v2 = 2KE/m
PE is converted to KE so KE = 85J
v2 = 2 (85J)/ 5.4 m
v2 = 31.481 . . . m2/s2
v = 5.6 m/s
4. What is the kinetic energy in J of an Argon
atom moving with a speed of 650 m/s? a mole of
Argon atoms moving with a speed of 650 m/s?
KE= 1/2 mv2
KE = 1/2 ( 6.63 x 10-23g)(650m/s)2
KE = 1.4 x 10
-20
J
KE = 1/2 (39.9g ) (650 m/s)2
KE = 8.4 x 103 J
5. Calculate the velocity of an electron whose
mass is 9.107 x 10-28 g and whose kinetic
energy is 1.585 x 10-17 J
KE = 1/2 mv2
V2 = 2KE/m
V2 = 2 (1.585 x 10-17J)/9.107 x 10-31 kg)
V2 = 3.4808 . . . x 1013m2/s2
V = 5.900 x 106 m/s
Chapter 6
26, 30, 32, 37, 41, 43, 45, 55, 59, 63,
71, 77, 79
FIRST LAW OF THERMODYNAMICS
Energy can be neither created nor destroyed.
Energy is conserved
INTERNAL ENERGY OF A SYSTEM
sum of all the KE and PE of all the components of
the system.
Internal energy is represented with the symbol E
Usually we don’t know the actual value of E
We hope to know the change in the E
FIRST LAW OF THERMODYNAMICS
Change in E = E
final
- E
initial
We don’t need the actual values for E final and
Einitial
only need the value for
Δ
Δ
E
E has three components
a number
a unit
a sign
When
Δ
E is positive it indicates
Efinal is greater than Einitial
Indicates that the system gained energy from the
surroundings
When
Δ
E is negative it indicates
Efinal is less than Einitial
Indicates that the system lost energy to the
surroundings
Initial state =
reactants
Final state =
products