Gases, liquids summary
Topics:
Properties of gases, ideal gas law, kinetic molecular model of
gases, nonideality, intermolecular forces, properties of liquids.
Definitions:
pressure, absolute zero, STP, molar volume, diffusion,
effusion, partial pressure, mean free path, root mean squared, inter/intra
molecular, hydrogen bond, dispersion forces, vapor pressure, boiling point,
viscosity, surface tension, capillary action, adhesion/cohesion
Calculations:
Ideal gas law static problems; ideal gas law comparison/
dynamic problems; combine ideal gas law with equations for mass, density,
molecular weight or with stoichiometry
Applications:
assign appropriate intermolecular force to a molecule
Ranking:
relative gas speeds; nonideality of gases, physical properties of
liquids, intermolecular force strength
Gases
•
For gases always work in Kelvin.
Temperature (K) = Temperature (˚C) + 273.15
•
STP = 1 atm, 0˚C
•
The
molar volume
of any ideal gas at STP = 22.414 L
•
Ideal Gas Law
:
PV = nRT
•
Boyle’s law (P,V), Charles’ law (P, T), and Avagadro’s law (V, n) can
all be derived from this
•
Static problems: we know three of the four variables, find the fourth.
•
Dynamic problems: one or more variables are perturbed while the
others are held constant.
Static problem:
What do we know?
What is unknown?
Do you need to use an equation to find n from m, M, MW, density?
Do you need to include stoichiometry?
Rearrange the ideal gas law with the unknown on one side.
Solve, doing appropriate unit conversions, specially T into Kelvin.
1. If we completely combust 6 moles of glucose
(C
6
H
12
O
6
) in the presence of excess oxygen in a 22
liter container at 25˚C, what would be the total final
pressure of the system in atmospheres?
2. If 56 g of liquid nitrogen evaporates at standard
temperature and pressure, what is the final volume of
the gaseous nitrogen?
1
2
3
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Dynamic or comparison problem:
What changes?
p, V
What stays constant? T, n
Write the initial ideal gas law with all constants on one side.
Write the final ideal gas law with all constants on one side.
Equate the two.
Rearrange so the unknown is one side.
Solve, doing appropriate unit conversions, specially T into Kelvin.
3. A sample of sulfur vapor at 100˚C exerts a pressure
of 0.75 atm on the walls of its container. If we heat
the container to 200˚C while holding all other
factors constant, what will be the resulting pressure
in the container due to the sulfur vapor?
A sample of sulfur vapor at 100˚C exerts a pressure of 0.75 atm on the
walls of its container. If we heat the container to 200˚C while holding all
other factors constant, what will be the resulting pressure in the
container due to the sulfur vapor?
Identify what changes?
T, p
Identify what stays constant?
V,n
Initial state equation:
= nRV = constant
T
1
p
1
Final state equation:
= nRV = constant
The two constants are equal
㱺
=
Rearrange and solve for the unknown: p
2
=
T
1
p
1
T
2
We can leave the units of
V and
p alone as long as they are the
same units for both states. We
must change T to Kelvin.
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 Spring '08
 wandelt
 Chemistry, Mole, Partial Pressure

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