Gases Laws Notes
Pressure
 Pressure- force per unit area caused by particles hitting the walls of a
container
 Barometer- Measures atmospheric pressure
 Atmospheric Pressure- Results from the weight of the air- mass of air
being pulled toward the center of the earth by gravity.
 Manometer- Measures pressure of a gas in a container
 Two types – Open and Closed
 Units for pressure: mm Hg, torr, Pascal (Pa), Kilopascal (kPa),
atmospheres (atm), pounds square inch (psi)
 1 atm = 760 mm Hg = 760 torr = 101325 Pa = 101.3 kPa = 14.69 psi
 Ex: You have 28 psi. How many atm? Torr? Pascals?

Learning Check: How many mmHg are 8.92atm?
Boyle’s Law
 Relationship between pressure and volume (constant temp.)
 Inverse proportion  P V
 P1V1= P2V2

Ex: Consider a 1.5 L sample of CCl2F2 at a pressure of 56 torr. If
pressure is changed to 150 torr at constant temperature, what is the new
volume?

Learning Check
Boyle’s Law variables:
Is Boyle’s Law an inverse or direct relationship?
Boyle’s Law constants:
Boyle’s Law formula:
Charles’ Law
 Relationship between volume and temperature (constant pressure)
 Inverse proportion  V T
oC + 273 = ____ K
 Temperature in Kelvin


V1 = V2
T1 T2
Ex: A 2.0 L sample of air is collected at 298 K and cooled to 278 K, the
pressure is held constant. What is the volume?

Learning Check
Charles’ Law variables:
Is Charles’ Law an inverse or direct relationship?
Charles’ Law constants:
Charles’ Law formula:
Gay-Lussac’s Law
 Relationship between pressure and temperature (constant volume)
 Inverse proportion  P T
oC + 273 = ____ K
 Temperature in Kelvin

P1 = P2
T1 T2

Ex A mylar balloon is filled with helium gas to a pressure of 107 kPa when
the temperature is 22 °C. If the temperature changes to is 45 °C, what
will be the pressure of helium in the balloon?

Learning Check
Gay-Lussac’s Law variables:
Is Gay-Lussac’s Law an inverse or direct relationship?
Gay-Lussac’s Law constants:
Gay-Lussac’s Law formula:
Avogardo’s Law
 Relationship between volume and moles (constant temp. and pressure)
 Inverse proportion  V n
n = #moles

V1 = V2
n1
n2

Ex: 12.2L sample contains 0.50 moles O2. If O2 is converted to O3, what
will the volume be?
3O22O3

Learning Check
Avogadro’s Law variables:
Is Avogadro’s Law an inverse or direct relationship?
Avogadro’s Law constants:
Avogadro’s Law formula:
Combined Gas Law
 Combination of Boyle’s law, Charles’ law and Gay-Lussac’s Law

P1 V1 = P2 V2
T1
T2

Ex: A 3.5 L sample of Argon exerts a pressure of 6.32 atm at 27 °C.
When the volume is increased to 4.7 L and the pressure is decreased to
4.15 atm, what is the final temperature?

Learning Check
Combined Gas Law variables:
Combined Gas Law constants:
Combined Gas Law formula:
A gas is heated from 263.0 K to 298.0 K and the volume is
increased from 24.0 liters to 35.0 liters by moving a large piston
within a cylinder. If the original pressure was 1.00 atm, what would
the final pressure be?
Ideal Gas Law
 PV = nRT


R = 0.08206 L* atm
mol * K
Ex: H2 has a volume of 8.56 L at 0oC and 1.5 atm.
Calculate the moles of H2 present.
P= pressure (atm)
V= volume (L)
n= Mole Gas (mol)
T=temperature (K)
R= universal gas constant
Learning Check: How many moles of gas are contained in a 2.00L flask at
98.8 kPa and 25.0°C?
Dalton’s Law of Partial Pressures
 Partial Pressure – pressure that a gas would exert if it alone in the
container.
 Ptotal = P1 + P2 + P3…
 Ex: A container holds three gases: oxygen, carbon dioxide, and helium.
The partial pressures of the three gases are 2.00 atm, 3.00 atm, and 4.00
atm, respectively. What is the total pressure inside the container?



A common method of collecting gas samples in the laboratory is to bubble
the gas into a bottle filled with water and allow it to displace the water.
When this technique is used, however, the gas collected in the bottle
contains a small but significant amount of water vapor. As a result, the
pressure of the gas that has displaced the liquid water is the sum of the
pressure of the gas plus the vapor pressure of water at that temperature.
The vapor pressures of water at various temperatures are given in Table.
PTotal - Pvapor = PGas
Learning Check
What does it mean to collect gas over water?
A sample of oxygen gas is collected over water. The total pressure
is 98.56 kPa. The partial pressure of the dry oxygen calculated to
be 95.70 kPa. What is the vapor pressure of water?
Gas Stoichiometry
 STP = Standard Temperature and Pressure
 Standard Temperature = 0oC
 Standard Pressure = 1 atm
 Molar Volume 1.00 molgas = 22.4 Lgas
 Ex 1: A sample of N2 has a volume of 1.75 L at STP. How many moles of
N2 are present?

Ex 3: Calculate the volume of CO2 produced at STP from 152g of CaCO3.
CaCO3  CaO + CO2

Ex 2: Calculate the volume of O2 produced at 1.00 atm and 25 oC by the
decomposition of 10.5g KClO3.
2KClO3  2KCl + 3O2

Challenge: What would the value of the Gas Constant, R, be with the
following units?
kPa*L
atm*L
mol*K
kmol*K