the behavior of gases part 2. ideal gases ideal gas law: ideal gas law: the relationship pv = nrt,...
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The Behavior of GasesThe Behavior of Gases
Part 2Part 2
Ideal GasesIdeal Gases
Ideal Gas Law:Ideal Gas Law: The relationship PV = nRT, which The relationship PV = nRT, which
describes the behavior of ideal gases.describes the behavior of ideal gases. Ideal Gas Constant (R):Ideal Gas Constant (R):
A term in the ideal gas law that is used A term in the ideal gas law that is used to make the units work out correctly.to make the units work out correctly.
Ideal GasesIdeal Gases
nRTPV M
mn
M
mRTPV
RT
PMD
V
m
Ideal GasesIdeal Gases
Example:Example: When the temperature of a rigid sphere When the temperature of a rigid sphere
containing 685 L of helium gas is held at containing 685 L of helium gas is held at 621 K, the pressure of the gas is 18,900 621 K, the pressure of the gas is 18,900 kPa. How many moles of helium does kPa. How many moles of helium does the sphere contain?the sphere contain?
Ideal GasesIdeal Gases
Example:Example: When the temperature of a rigid sphere When the temperature of a rigid sphere
containing 685 L of helium gas is held at containing 685 L of helium gas is held at 621 K, the pressure of the gas is 18,900 621 K, the pressure of the gas is 18,900 kPa. How many moles of helium does kPa. How many moles of helium does the sphere contain?the sphere contain?
V = 685 LV = 685 LT = 621 KT = 621 KP = 18,900 kPaP = 18,900 kPan = ?n = ?
Ideal GasesIdeal Gases
Example:Example: When the temperature of a rigid sphere When the temperature of a rigid sphere
containing 685 L of helium gas is held at containing 685 L of helium gas is held at 621 K, the pressure of the gas is 18,900 621 K, the pressure of the gas is 18,900 kPa. How many moles of helium does kPa. How many moles of helium does the sphere contain?the sphere contain?
Ideal GasesIdeal Gases
He 2510mol621K
molKkPaL
8.31
685L18900kPaRT
PVn
RT
nRT
RT
PV
nRTPV
Real Versus Ideal GasesReal Versus Ideal Gases
Do real gases behave in ideal ways?Do real gases behave in ideal ways?1.1. As they are compressed, the volume of the As they are compressed, the volume of the
individual real gas particles are significantindividual real gas particles are significant
2.2. Many real gases have intermolecular forcesMany real gases have intermolecular forces
3.3. Most real gases can be liquefied (or Most real gases can be liquefied (or solidified). An ideal gas can’t.solidified). An ideal gas can’t.
* Ideal behavior is most often seen at high * Ideal behavior is most often seen at high temperatures and low pressures.temperatures and low pressures.
Graham’s Law of Diffusion and Graham’s Law of Diffusion and EffusionEffusion
Diffusion:Diffusion: The process by which a gas expands to The process by which a gas expands to
fill the available volume; the random fill the available volume; the random walks of the gas particles take them in all walks of the gas particles take them in all directions. This is why an air freshener directions. This is why an air freshener makes the whole room smell good.makes the whole room smell good.
Effusion:Effusion: The process by which gas particles pass The process by which gas particles pass
through a small opening. This is why air through a small opening. This is why air leaves a tire with a nail hole in it.leaves a tire with a nail hole in it.
Graham’s Law of Diffusion and Graham’s Law of Diffusion and EffusionEffusion
Graham’s Law:Graham’s Law: The rate at which gases diffuse or effuse is The rate at which gases diffuse or effuse is
inversely proportional to the square root of inversely proportional to the square root of their molar masses.their molar masses.
1
2
2 gas ofeffusion of rate
1 gas ofeffusion of rate
M
M
Graham’s Law of Diffusion and Graham’s Law of Diffusion and EffusionEffusion
Example:Example: A sample of helium effuses through a A sample of helium effuses through a
porous container 6.50 times faster than porous container 6.50 times faster than does an unknown gas. What is the does an unknown gas. What is the molar mass of the unknown?molar mass of the unknown?
Graham’s Law of Diffusion and Graham’s Law of Diffusion and EffusionEffusion
Example:Example: A sample of helium effuses through a A sample of helium effuses through a
porous container 6.50 times faster than porous container 6.50 times faster than does an unknown gas. What is the does an unknown gas. What is the molar mass of the unknown?molar mass of the unknown?
RateRate11 = 6.50 = 6.50··RateRate22
MM11 = 4.00 g/mol = 4.00 g/mol
MM22 = ? = ?
mol
g16900.4
1
50.6
rate
rate
rate
rate
rate
rate
rate
rate
2
1
2
2
12
1
2
2
11
1
2
2
1
2
2
2
1
1
2
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1
MM
MMM
M
M
M
M
M