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LPH 105 W15 13 intro

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Richard Datwyler

on 5 July 2016

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Transcript of LPH 105 W15 13 intro

Temperature and Kinetic Theory
Atomic Theory
Temperature
Expansion
Ideal Gas Law
Kinetic Theory
Phases / diagrams
amu
Celsius, Fahrenheit, Kelvin
Atomic Theory
Everything made of atoms
phases describe by interacting atoms
solid : atoms bonded
liquids : week forces, motion allowed
gases : high speeds little interaction
amu, uamu, u
atomic mass number
Temperature
All scales need two things
starting point
step size
Conversions
273 is just fine.
Expansion
All things expand when heated, and shrink when cooled.
water is notable exception.
These are table problems. look up the alpha or beta values.
Ideal gas law
A. remember it with fondness
B. Remember it, not so fun
C. Have forgotten it
D. Never heard of it

Many experiments done over the years, sometimes with many years in between
P and V inversely proportional
V and T proportional
P and T proportional
(Kelvin scale)
Mass not the proportionality constant, Number of particle is.
moles
A mole is defined as the same number of atoms or molecules as there are in 12 grams of carbon 12

thus it is a unit of number,
Molecular mass. This is the number you read on a
periodic table below the element.
It is the amu of an element, or the number of grams
needed for a mole of the substance.

for example
carbon dioxide has 1 carbon and 2 oxygens
so its molecular mass is 12+16+16 = 44 u

And if I had 66 grams I would have 66/44 = 1.5 mol
How many moles of Carbon 12
do I have if the sample contains
48 grams?
A. 1
B. 2
C. 3
D. 4
E. 5

This is the equation of state for an ideal gas
often called the ideal gas law. Where R is the
proportionality constant
other number work, just watch units.

pressure is in Pa, volume in cubic meters
T in kelvin.
This is a powerful equation that is used for all gases, by adding up how many particles there are in a mole.

thus one way to define a mole is the number of particles, Avogadro's number.
It says that 1 mole = 6.022 x 10^23 particles
or that:
We can then write the ideal gas law
in terms of number of particles as well:




this introduces Boltzmann's constant
Kinetic Theory
The just of Kinetic theory is that
state variables: pressure, temperature,
volume, etc
can be described by atomic variables
microscopic defines macroscopic
There is a bit of a derivation that you can look up, but the first one comes to describe pressure from the motion of little particles.
It leads straight into the energy of a system of an ideal gas. Relating the kinetic energy of a
single molecule
to the state variable of temperature.
microscopic to macroscopic
From this, solve for the velocity.

Each molecule will move in different directions so they square it, then average all those numbers, and square root it, to get what is called the root mean squared velocity.
Note the mass is the mass of one molecule.
Phase diagrams
Note:
solid
liquid
gas
triple point
phase changes
This is when one substance is added into another and it randomly blends in, no mixing just motion of particles



Fick's law describes it to you.

Learn to recognize it. It is a plug and chug equation that uses a table.
Diffusion
Area, Distance, concentration difference, and diffusion constant gives rate of diffusion
Calculate the rms speed of helium atoms near the surface of the Sun at a temperature of about 6000 K
Calculate the density of oxygen at 1 atm and 0 C
Expansion
A concrete highway is built of slabs 12 m long (at 12 degrees C) how wide should the expansion cracks between the slabs be to prevent buckling if it ranges to temperatures up to 50 degrees C? (12 x 10^-6 C^-1)
5.5 mm
15 below zero on the Celsius scale is what on the Fahrenheit scale

15 below zero on the Fahrenheit scale is what on the Celsius scale?
-26 C
5 F
"I'm a little confused with the concept of Vrms and where the equation came from."
"What's the difference between kinetic theory and kinematics or are closely they related somehow?"
" Can we thoroughly go over moles? "
"Okay, first of all... zeroth? Anyway, I don't really get how that law is very useful to us. Can we go over it in more depth?"
"I don't understand the kinetic molecular theory equation. "
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