Unit 14 Unit 14 Gas Laws
Dec 28, 2015
Unit 14Unit 14
Gas Laws
Properties of GasesProperties of Gases
Gas properties can be Gas properties can be modeledmodeled using math. using math. Model depends on—Model depends on—
1.1. V = volume of the gas (L)V = volume of the gas (L)
2.2. T = temperature (Kelvin, K)T = temperature (Kelvin, K)
3.3. n = amount (moles, mol)n = amount (moles, mol)
4.4. P = pressure (atmospheres, atm)P = pressure (atmospheres, atm)
STP
STP = standard temperature and pressure
Standard temperature = 0°C = 273 K
Standard pressure = 1 atm
Pressure of a Gas
SI unit of pressure: pascal (Pa)Other common pressure units:
Millimeters of mercury (mm Hg) Atmospheres (atm)
1 atm = 760 mmHg = 101.3 kPa = 760 torr
Practice Converting Units
1 atm = 760 mmHg = 101.3 kPa
A tire pressure gauge records a pressure of 450 kPa. What is the pressure in atmospheres? In mm Hg?
RELATIONSHIP BETWEEN PRESSURE AND VOLUME
Boyle’s Law
Boyle’s Law in Real Life
Popping a balloon As you squeeze the balloon, what happens
to the pressure and volume inside the balloon?
Are pressure and volume directly proportional or inversely proportional?
P V
Boyle’s Law in Real Life
Operating a water gun/syringe As you pull back on the plunger, are you
increasing or decreasing the volume? How does the pressure change?
Are P and V directly or inversely proportional?
P V
Boyle’s Law in Real Life
Marshmallow/balloon in a vacuum As we evacuate the chamber, what do you
think will happen to the pressure? What do you think will happen to the volume of the marshmallow?
Are P and V directly or inversely proportional?400 Marshmallows in a Vacuum
P V
Boyle’s Law
When temperature is held constant, pressure and volume increase and decrease as opposites
Pressure & volume are inversely or indirectly related If pressure increases, volume decreases If pressure decreases, volume increasesP1V1 =
P2V2
Practice with Boyle’s Law
A balloon contains 30.0 L of helium gas at 103 kPa. What is the volume of the helium when the balloon rises to an altitude where the pressure is only 25.0 kPa? (Assume temperature is held constant)P1V1 = P2V2
P1 =
V1 =
P2 =
V2 =
Practice with Boyle’s Law
At room temperature, 10.01 L of a gas is found to exert 97.0 kPa. What pressure (in atm) would be required to change the volume to 5.00 L?P1V1 = P2V2
P1 =
V1 =
P2 =
V2 = 1 atm = 101.3 kPa
Practice with Boyle’s Law
Nitrous oxide (N2O) is used as an anesthetic. The pressure on 2.50 L of N2O changes from 105 kPa to 40.5 kPa. If the temperature does not change, what will the new volume be?P1V1 = P2V2
P1 =
V1 =
P2 =
V2 =
CHARLES’ LAW:
Relating Volume and Temperature
Charles’ Law in Real Life
Balloons popping when kept outdoors As the balloons sits outside, what happens to
the temperature of the gas inside the balloon? What happens to the volume of the balloon?
Are volume and temperature directly proportional or inversely proportional?
V T
Charles’ Law in Real Life
A ball outside on a cold day You pump the ball up indoors. After
going outside where it’s colder, what happens to the volume of the ball?
Are volume and temperature directly or inversely proportional?
V T
Charles’ Law in Real Life
Liquid Nitrogen demo video When the balloon is placed in the liquid
nitrogen, what happened to the temperature of the gas inside the balloon? What happened to the volume?
Are volume and temperature directly or inversely proportional?
V T
Charles’ Law
If pressure is held constant (doesn’t change), volume and temperature increase or decrease together If volume increases, so does the
temperature If temperature decreases, so does the
volume
2
2
1
1
T
V
T
V ***T must
be in Kelvin!!!
Practice with Charles’ Law
A balloon inflated in a room at 24 ºC has a volume of 4.00 L. The balloon is then heated to a temperature of 58 ºC. What is the new volume if the pressure remains constant?
V1 =
T1 =
V2 =
T2 =2
2
1
1
T
V
T
V
Practice with Charles’ Law
Exactly 5.00 L of air at -50 ºC is warmed to some temperature so that the volume was 8.36 L. What temperature was the system warmed to?
V1 =
T1 =
V2 =
T2 =2
2
1
1
T
V
T
V
Practice with Charles’ Law
A 50.0 mL sample of a gas is cooled from 119 ºC to 353 K. If the pressure remains constant, what is the final volume of the gas?
V1 =
T1 =
V2 =
T2 =2
2
1
1
T
V
T
V
Gay-Lusaac’s Law:The Relationship Between Pressure and Temperature
Gay-Lusaac’s Law in Real Life
Warnings on aerosol cans What do the warnings say regarding putting
them near flames? As the temperature of the can increases, what
happens to the pressure in the can?
Are pressure and temperature directly or inversely proportional?
P T
Gay-Lusaac’s Law in Real Life
Warm soda fizzing vs. cold soda fizzing When opened, which one fizzes more, cold
soda or warm soda? Does more fizzing mean there was higher
pressure inside or lower pressure?
Are pressure and temperature directly or inversely proportional?
P T
Gay-Lusaac’s Law in Real Life
Egg and flask demo When the boiling water gets dumped goes out,
what happens to the temperature of the gases inside the flask?
Do the gas particles have more kinetic energy or less? Are they creating more pressure or less?
Are pressure and temperature directly or inversely proportional?
P T
Gay-Lusaac’s Law
If volume is held constant, pressure and temperature increase and decrease together If pressure increases, so does the temperature If temperature decreases, so does the pressure
2
2
1
1
T
P
T
P
Practice with Gay-Lusaac’s Law
The gas in a used aerosol can is at a pressure of 103 kPa at 25 ºC. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928 ºC?
P1 =
T1 =
P2 =
T2 =
2
2
1
1
T
P
T
P
Practice with Gay-Lusaac’s Law
A sample of nitrogen has a pressure of 6.58 kPa at 539 K. If the volume does not change, what will the pressure be at 211 K?
P1 =
T1 =
P2 =
T2 =
2
2
1
1
T
P
T
P
Practice with Gay-Lusaac’s Law
A 10.01 L sample of a gas is found to exert 97.0 kPa at 25 ºC. What temperature (in celsius) would be required to change the pressure to 1.00 atm?
P1 =
T1 =
P2 =
T2 =2
2
1
1
T
P
T
P
The Combined Gas Law
Taking Into Account Pressure, Volume, AND Temperature
In Review
Boyle’s Law looked at which 2 factors?
Charles’ Law?
Gay Lusaac’s?
Imploding Can Demo
What happened to the volume of the can?
What happened to the temperature of the gas inside the can?
How did pressure play a role in the can imploding?
The Combined Gas Law
The combined gas law considers the effect of all 3 factors at the same timeAll 3 of the gas laws can be derived from
the combined gas law
2
22
1
11
T
VP
T
VP
Example – Boyle’s Law from Combined Gas Law
If temperature is constant, T1 = T2
Rearrange the equation to get both temperatures together
Examples with Combined Gas Law
A 200 mL sample of gas is collected at 50 kPa and a temperature of 271oC. What volume would this gas occupy at 100 kPa and a temperature of -14oC?
2
22
1
11
T
VP
T
VP
Examples with Combined Gas Law
Helium in a 100 mL container at a pressure of 66.6 kPa is transferred to a container with a volume of 250 mL. What is the new pressure if the temperature changes from 20oC to 15oC?
2
22
1
11
T
VP
T
VP
Examples with Combined Gas Law
A certain sample of gas has a volume of 0.452 L measured at 87oC and 0.620 atm. What is its volume at 1 atm and 0oC?
2
22
1
11
T
VP
T
VP
The Ideal Gas LawP, V, T, and n
The Combined Gas Law
Takes into account P, T, and V but not the amount of gas present Amount of gas = moles of gas present (n)
2
22
1
11
T
VP
T
VP
Takes into account all 4 variables – pressure (P), volume (V), temperature (T), AND the amount of moles (n)
R = 0.0821 = 8.314 =
The Ideal Gas Law
nRTPV
Kmol
atmL
Kmol
kPaL
Ideal Gas
Constant
Sample Problem – Ideal Gas LawHow many moles are in a sample of gas occupying 12 L at a temperature of 15˚C and a pressure of 2.4 atm?
PV = nRT
The Ideal Gas Law Once you calculate the moles of gas you
can convert this to a mass (in grams, kilograms, etc.) using what?
You may also be given the amount of gas in grams and have to convert it to moles in order to plug into the ideal gas law
Sample Problem – Ideal Gas Law
What is the volume occupied by 36.0 grams of water vapor at 125C and 102 kPa?
PV = nRT
Sample Problem – Ideal Gas Law
What mass of carbon dioxide will occupy 5.5 L at 5C and 0.74 atm?
PV = nRT
Sample Problem – Ideal Gas LawA deep underground cavern contains 2.24 x 106 L of methane gas (CH4) at a pressure of 1500 kPa and a temperature of 315 K.
(a) How many moles of CH4 does the cavern contain? (b) How many kilograms does the cavern contain?
PV = nRT
Ideal Gases vs. Real Gases Ideal Gas – a gas which behaves
according to the gas laws and KMT at all pressures and temperatures Gas particles have no volume and no
attraction to one another No such thing as an ideal gas; just real
gases which behave like ideal gases under certain conditions
Ideal Gases vs. Real Gases Real gases behave like ideal gases under
the following conditions: At high temperature At low pressure When the gas itself has small, non-polar
molecules
Why??