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CH302 Vanden Bout/LaBrake Fall 2012
Vanden Bout/LaBrake
CH301
THERMODYNAMICS HEAT AND WORK
UNIT 4 Day 1
CH302 Vanden Bout/LaBrake Spring 2012
Important Information
LM26 & LM27 DUE T 9AM
LM26 CONTAINS A WORKSHEET – YOU SHOULD COMPLETE THE WORKSHEET
EXAM GRADES SHOULD BE POSTED BYEND OF DAY FRIDAY
UNIT4DAY1-LaBThursday, November 08, 20128:22 AM
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CH302 Vanden Bout/LaBrake Fall 2012
What are we going to learn today?
Chemical and Physical changes are accompanied by changes in energy
Energy moves in the form of heat and work
Get a feel for heat and work
Get a feel for energy units
CH302 Vanden Bout/LaBrake Fall 2012
EVERY change – physical or chemical -is accompanied by a change in energy
Energy is conserved, so it is just getting movedaround from one form to another
The First Law of Thermodynamics
ENERGY
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CH302 Vanden Bout/LaBrake Fall 2012
When I think of types of energy, I think:a) KE and PE are the same as heat & workb) PE and KE are the same as heat & workc) PE and KE are the only two forms of energyd) Heat and work are the only two forms of energy
POLL: CLICKER QUESTION 1
CH302 Vanden Bout/LaBrake Fall 2012
When I think of types of energy, I think:
WHAT IT IS:PE - energy due to position or compositionKE - energy of the motion of an object or particle
HOW IT MOVES:Heat - transfer of energy from a hotter body to a colder bodyWork – transfer of energy via applied force over distance
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CH302 Vanden Bout/LaBrake Fall 2012
STAND ON A CHAIR
DROP A BALL TO THE FLOOR
DESCRIBE ENERGY OF BALL
CHEMICAL CHANGE -
A BIT MORE OF A CHALLENGE TO VISUALIZE
CH302 Vanden Bout/LaBrake Fall 2012
ORGANIZE OBSERVATIONS – SYSTEM & STATE
DEFINE SYSTEM & SURROUNDINGS
DESCRIBE BEGINNING AND END “STATE”
DESCRIBE CHANGE = STATEend – STATEbeginning
CH302 Vanden Bout/LaBrake Fall 2012
DEMONSTRATE ENERGY ON THE MOVE
Physical Change – Doing Work
Physical Change – Absorbing Heat
Chemical Change – Giving off Heat
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CH302 Vanden Bout/LaBrake Fall 2012
DEMONSTRATE ENERGY ON THE MOVE
Physical Change – Doing Work
Physical Change – Absorbing Heat
Chemical Change – Giving off Heat
CH302 Vanden Bout/LaBrake Fall 2012
BURN FOSSIL FUELS – ENERGY CHANGES
POWER PLANT
AUTOMOBILE
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CH302 Vanden Bout/LaBrake Fall 2012
OBSERVE, MODEL, QUANTIFY
Chemist cares about understanding and quantifying the
amount of energy that moves into or out of a system
upon a change.
“THERMODYNAMICS”
Energy moves in the form of HEAT and WORK
CH302 Vanden Bout/LaBrake Fall 2012
First Law of Thermodynamics –
LAW OF CONSERVATION OF ENERGY
UNIVERSE = SYSTEM + SURROUNDINGS
YOU DEFINE YOUR SYSTEM, EVERYTHING ELSE IS
SURROUNDINGS
ΔU = q + w
ENERGY IS CONSERVED IN THE UNIVERSE
CH302 Vanden Bout/LaBrake Fall 2012
HEAT = q
Gummy bears
calorie – the amount of energy it takes to raise the
temperature of 1 gram of water 1 degree C.
Kilocalorie (Calorie)
Joule
MODEL & QUANTIFY HEAT
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CH302 Vanden Bout/LaBrake Fall 2012
HEAT = q
Gummy bears
calorie – the amount of energy it takes to raise the
temperature of 1 gram of water 1 degree C.
Kilocalorie (Calorie)
Joule
MODEL & QUANTIFY HEAT
CH302 Vanden Bout/LaBrake Fall 2012
MODEL & QUANTIFY HEAT
HEAT = q
Heat is energy transferred as a result of temperature difference
Temperature is a property that reflects the random motions of the particles in a particular substance.
q is the symbol used to indicate energy changed by receiving or losing heat
q is “+” when system receives heat from surroundings q is “-” when heat is given off by system to surroundings
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CH302 Vanden Bout/LaBrake Fall 2012
MODEL & QUANTIFY WORK
WORK = w
MOSTLY CARE ABOUT “PV” WORK
THINK OF AN EXAMPLE OF “PV” WORK
CH302 Vanden Bout/LaBrake Fall 2012
Today you saw a demonstration in which a piece of solid carbon dioxide was placed in a container and the lid popped off the container after a few minutes. In this situation:
a) HEAT was transferred INTO the system, WORK was done BY the system.b) HEAT was transferred OUT OF the system, WORK was done BY the system.c) HEAT was transferred INTO the system, WORK was done ON the system.d) HEAT was transferred OUT OF the system, WORK was done ON the system.e) HEAT was NOT transferred, ONLY WORK was done BY the system.
POLL: CLICKER QUESTION 2
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CH302 Vanden Bout/LaBrake Fall 2012
Expansion work – expand against an external force
Work done by system is “-”Work don on system is “+”
w = - PexΔV
Example: The gases in the four cylinders of an automobile engine expand from 0.22 L to 2.2 L during one ignition cycle. Assuming that the gear train maintains a steady pressure of 9.60 atm on the gases, how much work can the engine do in one cycle?
QUANTIFY WORK
CH302 Vanden Bout/LaBrake Fall 2012
ΔU = q + w
Quantify q & state the sign of qQuantify w & state the sign of w
This tells a detailed energy story about your system
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CH302 Vanden Bout/LaBrake Fall 2012
A system absorbs 72 J of heat while 35 J ofwork is done on it. Calculate ΔU.
POLL: CLICKER QUESTION 3
CH302 Vanden Bout/LaBrake Fall 2012
A system was heated by using 600 J of heat, yet it was found that the internal energy decreasedby 150 J . Calculate w.
Was work done on the system or by the system?
POLL: CLICKER QUESTION 4
CH302 Vanden Bout/LaBrake Fall 2012
• A balloon is inflated to its full capacity by heating the air inside it. In the final stages of this process the volume of the balloon changes from 4.00X106 L to 4.50X106 L by the addition of 1.3X108 J of energy as heat. Assuming the balloon expands against a constant pressure of 1.0 atm, calculate the ΔE for the process.
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CH302 Vanden Bout/LaBrake Fall 2012
• A balloon is inflated to its full capacity by heating the air inside it. In the final stages of this process the volume of the balloon changes from 4.00X106 L to 4.50X106 L by the addition of 1.3X108 J of energy as heat. Assuming the balloon expands against a constant pressure of 1.0 atm, calculate the ΔE for the process.
CH302 Vanden Bout/LaBrake Fall 2012
• A property with a value that depends only on the current state of the system and is independent of the manner in which the state was prepared. Look back at ball A.
– IMPORTANT POINT IS: if the system is changed from one state to another, the change in a state function is independent of how that change was brought about! (E is a state function, w and q are not state functions!)
State Functions ΔX = Xf - Xi
CH302 Vanden Bout/LaBrake Fall 2012
Extensive
Intensive
State Function
System
Surroundings
Universe
Vocabulary Check
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CH302 Vanden Bout/LaBrake Fall 2012
Extensive
Intensive
State Function
System
Surroundings
Universe
Vocabulary Check
CH302 Vanden Bout/LaBrake Fall 2012
WHAT HAVE WE LEARNED TODAY?
First Law of Thermodynamics: Energy is conserved in universe- Law of Conservation of Energy
ΔU = q + w
Heat – movement of energy from hotter body to colder bodyWork – force x distance – PΔV
Sign convention important“-” work done by system “+” work done on the system
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CH302 Vanden Bout/LaBrake Fall 2012
Learning Outcomes
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