# Intro to Gas Laws Presentation

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Gas Laws
What are the typical behaviors
of (ideal) gases?
Why do gases behave the way
they do?
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Why is it important to
before flying...?
When (and why) should you
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Important ideas:
The Gas Laws:
Gay­Lussac's Law
(Temp + pressure)
Dalton's Law of Partial Pressures
(Avog's law)
Boyle's law
(volume + pressure)
Charles' Law
(volume + temperature)
Combined Gas Law
Ideal Gas Law
Phase diagram
(Incorporates Pressure)
Entropy of a system
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What is Pressure?
Hint: Have you ever measured the pressure in your tires? What are the units?
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Pressure is any force applied over a certain area.
A greater force produces a greater _ F_
pressure, and a smaller P = A area results in a greater pressure.
Ex: single nail vs. bed of nails
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What causes the force in a gas?
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Hint: How is the gas composed/ what is happening at a level which is not visible?
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Kinetic Molecular Theory
(KMT)
1) Particles are discrete and have negligible volume­points in space
2) Particles do not interact in any appreciable manner, except to collide occasionally
(elastic collisions)
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Particles in a container
(2­D)
The particles move in straight lines until
they meet (collide) with other particles or
the walls of the container
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"Kinetic" = motion
Kinetic Energy
1 2
KE = mv
2
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Temperature is the measure of the average kinetic energy of motion in the particles
Some of the particles will be moving very quickly, and others barely at all, so it is the average (think of histograms or bell curves­­the temp will be closest to the highest bar or the peak of the bell)
Generally, we think of temperature as resulting from the speed of the particles, as that has the greater effect, but mass also affects the KE. Larger particles will not move as quickly, but ultimately we concentrate on the speed and not the mass for a given sample­­mass it not as significant as speed in measuring temp.
In many cases, the gas is not a mixture, so different masses would not be a factor anyway.
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Gay­Lussac
(Direct proportion b/t temp +
pressure of a gas)
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Gay­Lussac's Law Expressed Mathematically:
P1/ T1 = P2/ T2
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Dalton's law of Partial Pressures
The individual pressure of each
gas in a system combines (totals)
to a sum = the total pressure
(air pressure)
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Mathematical definition
Avogadro's law is stated mathematically as:
Where:
V is the volume of the gas(es).
n is the amount of substance of the gas.
k is a proportionality constant.
The most significant consequence of Avogadro's law is that the ideal gas constant has the same value for all gases.
This means that:
Where:
p is the pressure of the gas in the sample and
T is the temperature of the gas in the sample
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Avogadro's Hypothesis states: Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Avogadro's Law states: The volume of a gas maintained at constant temperature and pressure is directly proportional to the number of moles of the gas (n). Avogadro's Law is expressed by the equation: Gas Laws F2017 TEXT
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Sample Problem: The volume of a sample of chlorine gas, Cl2, is 9.42 liters at STP. What is the mass of the sample, in grams? Hint: When conditions are at STP, it is known that 1 mole of any gas occupies 22.4 liters. We can assume this as V1 and n1.
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Boyle's law
Pressure + Volume have an
inverse relationship
(Temp, amount of gas are constant)
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Charles' Law
Relation b/t Temperature
and Volume
Direct
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Combined Gas law
(we assume the amount of the gas, n,
remains constant)
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Combined Gas law
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Ideal gas Law
PV=nRT
R is the gas constant
If P is in atm
V is in L
n is in mol
T is in K
R = 0.0821
If P is in Pa (Pascals)
R=8.31
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PV=nRT
at any given instant
assuming no change
constant
at time 1
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If constant T
Boyle's law
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If const. V ("rigid container")
Gay­Lussac's law
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If constant P
Charles' Law,
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