Transcript GAS LAWS

GAS LAWS
HOW PRESSURE, TEMPERATURE AND VOLUME RULE THE WORLD
I. Kinetic Molecular Theory
A. gas particles are in constant, random motion
B. assume no volume or attractive forces
C. move in straight lines
D. Movement directly proportional to temperature
1. Temperature must be in
Kelvin
Kelvin = °C + 273
Celsius = K - 273
2. Absolute zero – the lowest temperature
theoretically possible. 0K
II. Gas Pressure
-measured as the force and quantity of impacts of a
gas on the walls of a container
-vacuum-absence of collisions and/or particles
-atmospheric pressure decreases as altitude increases
due to fewer gas particles
1 atm = 101.3kPa = 760mmHg
III. Gas Laws
A. 4 variables that interact
1. Pressure (P) – kPa, atm, mmHg
2. Volume (V) – mL or L
3. Temperature (T) – K
4. Moles (n) - moles
B. Quantity of Gas
1. as number of particles increase, so does
possibility of collisions, increasing pressure
C. Volume
1. Decreasing the size of a container gives
particles less distance to travel, increasing the
number of potential wall collisions and
increasing pressure
D. Temperature
1. increasing the temperature increases the
kinetic energy (thus amount of movement) in a
substance. Faster moving = more collisions
and increase force of collisions, increasing
pressure
E. Boyles Law – Pressure/Volume Relationship
1. Inversely proportional relationship
a. When pressure goes up, volume goes
down
P1V 1 = P 2 V2
Ex. What is the pressure of a balloon that starts out at
678mmHg and 45mL, when the volume increases to
123mL?
P 1V 1 = P 2V 2
(678mmHg)(45mL) = P2(123mL)
P2 = 248.05mmHg
*because both final and initial volumes were given
in mL, there was no need to convert
F. Charles Law – Volume/Temperature
Relationship
1. Directly proportional relationship
a. When temperature goes up, volume goes
up
as well
V1/T1 = V2/T2
Ex. A container with a volume of 5.4L at 23°C is
heated to 283°C. What is the final volume?
23ºC + 273 = 296K
283ºC +273 = 556K
5.4L/296K = V2/556K
V2 = 10.1L
G. Gay-Lussac’s Law – Pressure/Temperature
Relationship
1. Directly proportional relationship
a. When temperature increases, so does
pressure
P1/T1 = P2/T2
Ex. What will the final temperature (in ºC)of a gas
be if it began at 13ºC at 100.9kPa and was
compressed until it was 23.4kPa?
H. These 3 laws can be combined into the
Combined Gas Law
**can memorize just this law, and eliminate any
variable that doesn’t change to get the law you
need
P 1V 1 = P 2V 2
T1
T2
Ex. A hot air balloon has a volume of 124L at STP.
What will the volume be when it ascends to an
altitude with a pressure of .25atm and a
temperature of -15ºC?
P1V1/T1 = P2V2/T2
(1atm)(124L) = (.25atm)(V2)
273K
258K
= 470L
I. Ideal Gas Law - relates the 3 variables you have
already seen to number of particles (moles)
-an ideal gas cannot be liquified or solidified
PV=nRT
P = pressure – must be in atm
V = volume – must be in L
n= moles – must be in moles
R = gas law constant (.0821 L atm/mol K)
T = temperature – must be in K
Ex. You fill a rigid steel cylinder that has a volume of
20.0L with nitrogen gas (N2) to a final pressure of
2.00x104kPa at 28.0C. How many moles of N2 does
the cylinder contain?
PV=nRT
2.00x104kPa = 197.4atm
28C+273 = 301K
197.4atm)(20.0L) = n(0.0821L atm/mol K) (301K)
(197.4)(20.0) = n
(0.0821)(301)
n = 160 mol N2
1. turns out we have not been telling you the
truth. Gases have properties that affect the
outcome of an expected value
-You will not have to calculate the impact, but you
will need to describe the effect.
a. 2 factors can influence results: attractions
and volume
1. gases can have attractions which draws
them closer than would be expected. This
occurs at lower temperatures.
a. Decreasing temperature slows the
molecules down, allowing attractions to
form. Low pressure allows molecules to
spread out. This means the volume of the
gas molecule is negligible compared to
the overall volume.
2. the actual volume of gas molecules
contributes to create a volume greater than
expected
a. At high pressure, the particles are
compressed creating a situation where
the volume of the molecule becomes
important. At high temperatures, the
particles move fast enough to negate
attractions.
J. Avogadro’s Law – equal numbers of molecules
of gas occupy the same volume, regardless of
the size of the molecules (MOLE!)
K. Dalton’s Law – the partial pressure of each gas
in a mixture adds up to the total pressure of the
mixture.
Ptotal = P1 + P2 + P3 +….
Ex. What is the pressure of air, which is composed of
79.10kPa for N2, .040kPa CO2, .94kPa other gases and
21.22kPa O2.
Ptotal = 79.10 + .040kPa + .94kPa + 21.22kPa = 101.30kPa
L. Graham’s Law – gases with lower molecular mass
effuse at a faster rate than heavier molecules
1. diffusion – tendency of molecules to move
towards areas of lower concentration to reach
equilibrium
2. effusion – the process in which a gas escapes
though a small hole in a container
RateA = molar massB
RateB = molar massA