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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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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


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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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


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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STAND ON A CHAIR

DROP A BALL TO THE FLOOR

DESCRIBE ENERGY OF BALL

CHEMICAL CHANGE -

A BIT MORE OF A CHALLENGE TO VISUALIZE


ORGANIZE OBSERVATIONS – SYSTEM & STATE

DEFINE SYSTEM & SURROUNDINGS

DESCRIBE BEGINNING AND END “STATE”

DESCRIBE CHANGE = STATEend – STATEbeginning


DEMONSTRATE ENERGY ON THE MOVE

Physical Change – Doing Work

Physical Change – Absorbing Heat

Chemical Change – Giving off Heat

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DEMONSTRATE ENERGY ON THE MOVE

Physical Change – Doing Work

Physical Change – Absorbing Heat

Chemical Change – Giving off Heat


BURN FOSSIL FUELS – ENERGY CHANGES

POWER PLANT

AUTOMOBILE

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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


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


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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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




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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MODEL & QUANTIFY WORK

WORK = w

MOSTLY CARE ABOUT “PV” WORK

THINK OF AN EXAMPLE OF “PV” WORK


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.


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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


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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A system absorbs 72 J of heat while 35 J ofwork is done on it. Calculate ΔU.



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?



• 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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• 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.


• 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


Extensive

Intensive

State Function

System

Surroundings

Universe

Vocabulary Check

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Extensive

Intensive

State Function

System

Surroundings

Universe

Vocabulary Check


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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Learning Outcomes

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