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Topics 3.1 & 3.2.9-3.2.12
Chapters 13.1-3,11; 14.1-2,7-9
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At a microscopic level, temperature is regarded as a
measure of the average kinetic energy per molecule
associated with its movement in the substance
Temperature
Internal Energy Materials have internal energy (U)
Internal energy of a body is the total energy associated with
the thermal motions of the particles
Can be comprised of both Ekand Epassociated with
particle motion
Ekcomes from the translational and rotational motion
of molecules
Epcomes from the forces between the molecules
(bonding, intermolecular forces, etc.)
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The term thermal energy or heat represents non-
mechanical energytransfer
between a system andits surroundings due to a temperature difference
Occurs from higher to lower temperature regions
Incorrect to refer to the thermal energy of/in an
object
Occurs between TWO objects
Heat is the flow of thermal energy from one object
to another Increases the internal energy of the receiver
Decreases the internal energy of the donor
Thermal Energy/Heat
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Heat can be transferred from one body to another
by: Conduction (contact)
Convection (through a fluid)
Radiation (from electromagnetic radiation, photons)
Methods of Heat Transfer
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Conduction An exchange of energy between microscopic particles by
collisions Less energetic particles gain energy during collisions with
more energetic particles
Rate of conduction depends upon the characteristics of the
substance In general, metals are good conductors
Contain large numbers of electrons that are relatively
free to move through the metal
Transport energy from one region to another
Conduction can occur only if there is a difference in
temperature between two parts of the conducting medium
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When two bodies are placed in contact, heat flows from the
warmer body to the colder body until the two objects reach
the same temperature
At thermal equilibrium, NET energy flow is zero
Energy flow has not stopped
Thermal Equilibrium
Thermometers Devices used to measure the temperature of an object or a
system
Make use of physical properties that change withtemperature
Many physical properties can be used
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Thermometers can be calibrated by placing them in thermal contact
with an environment that remains at constant temperature
Celsius Scale
The upper fixed point is the boiling point of pure water at
atmospheric pressure (set to 100 oC)
The lower fixed point is the melting point of pure water at
atmospheric pressure (set to 0 oC) Scale between them was divided by 100 to give individual degrees
Kelvin Scale
Based on atomci level (no negative Kelvin temperature)
When the pressure of a gas goes to zero, its temperature is273.15 oC This temperature is called absolute zero
Absloute zero corresponds to no motion at the atomic level
To convert: TK = TC+ 273.15
Temperature Scales
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Amount of a substance which contains the same
number of elementary entities as there are in 12grams of carbon-12
1mole = 6.02x1023particles/molecules/atoms/ions
Denoted By NAand called Avogadro constant
The Mole
Molar MassMolar mass is the mass of 1 mole of the substance
SI unit: kg mol-1
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Concept that matter is made up of atoms which are
in continual random motion is called kinetic theoryThis leads to the idea of pressure
Particles collide with the walls of the container
Particles change their momentum and exert a force
on the wall
This creates pressure
Collisions of the molecules with the container (not
with each other) create the pressure
Kinetic Theory
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Ideal gas is a theoretical gas that obeys the gas laws and
thus fit the ideal gas equation exactly Real gases conform to the gas laws under certain limited
conditions
But they condense to liquids and then solidify if the
temperature is lowered Furthermore, there are relatively small forces of
attraction between particles of a real gas
Ideal Gas vs. Real Gas
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To make a real gas obey ideal gas laws, the following
assumptions are made about he molecules in a gas:
1. Gases consist of a very large number of tiny particles
called atoms or molecules moving in random directions
with a variety of speeds
2. On average, molecules are far apart from one another(much larger than their diameter) so that the range of
intermolecular forces is small compared with the distance
between them
3. No forces act between particles except during collisions4. Molecules are assumed to obey Newtons Laws and are
assumed to interact only when they collide
5. All collisions are assumed to be perfectly elastic
Kinetic Model of Ideal Gas
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The kinetic theory relates the macroscopic behavior
of an ideal gas to the microscopic behavior of itsmolecules or atoms
HOMEWORK:
1. How are pressure and temperature related? Explain
using kinetic theory.
2. How are pressure and volume be related? Explain
using kinetic theory.3. How are volume and temperature related? Explain
using kinetic theory.
Kinetic Theory