Gas Laws F2017 TEXT
November 27, 2017
Gas Laws
What are the typical behaviors
of (ideal) gases?
Why do gases behave the way
they do?
Gas Laws F2017 TEXT
November 27, 2017
Why is it important to
remember your chewing gum
before flying...?
When (and why) should you
check your tire pressure?
Gas Laws F2017 TEXT
November 27, 2017
Important ideas:
The Gas Laws:
Gay­Lussac's Law
(Temp + pressure)
Dalton's Law of Partial Pressures
Avogadro's hypothesis
(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
Gas Laws F2017 TEXT
November 27, 2017
What is Pressure?
Hint: Have you ever measured the pressure in your tires? What are the units?
Gas Laws F2017 TEXT
November 27, 2017
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
Gas Laws F2017 TEXT
November 27, 2017
What causes the force in a gas?
Gas Laws F2017 TEXT
Hint: How is the gas composed/ what is happening at a level which is not visible?
November 27, 2017
Gas Laws F2017 TEXT
November 27, 2017
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)
Gas Laws F2017 TEXT
November 27, 2017
Particles in a container
(2­D)
The particles move in straight lines until
they meet (collide) with other particles or
the walls of the container
Gas Laws F2017 TEXT
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"Kinetic" = motion
Kinetic Energy
1 2
KE = mv
2
Gas Laws F2017 TEXT
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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.
Gas Laws F2017 TEXT
November 27, 2017
Gay­Lussac
(Direct proportion b/t temp +
pressure of a gas)
Gas Laws F2017 TEXT
November 27, 2017
Gay­Lussac's Law Expressed Mathematically:
P1/ T1 = P2/ T2
Gas Laws F2017 TEXT
November 27, 2017
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)
Gas Laws F2017 TEXT
November 27, 2017
Avogadro's Law
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
Gas Laws F2017 TEXT
November 27, 2017
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
November 27, 2017
Gas Laws F2017 TEXT
November 27, 2017
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.
Gas Laws F2017 TEXT
November 27, 2017
Gas Laws F2017 TEXT
November 27, 2017
Boyle's law
Pressure + Volume have an
inverse relationship
(Temp, amount of gas are constant)
Gas Laws F2017 TEXT
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Charles' Law
Relation b/t Temperature
and Volume
Direct
Gas Laws F2017 TEXT
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Combined Gas law
(we assume the amount of the gas, n,
remains constant)
Gas Laws F2017 TEXT
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Combined Gas law
Gas Laws F2017 TEXT
November 27, 2017
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
Gas Laws F2017 TEXT
November 27, 2017
PV=nRT
at any given instant
assuming no change
constant
at time 1
Gas Laws F2017 TEXT
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If constant T
Boyle's law
Gas Laws F2017 TEXT
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If const. V ("rigid container")
Gay­Lussac's law
Gas Laws F2017 TEXT
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If constant P
Charles' Law,
Gas Laws F2017 TEXT
November 27, 2017