High School
SAT
ACT
University
MCAT
LSAT
DAT
Wize University Chemistry Textbook > Gases and their Properties

Graham's Law of Effusion

Gas Mixtures & Partial PressuresPrevious Section
Kinetic Energy, Temperature, and Speed of Gas ParticlesNext Section
Popular Courses
Find My Course
0:00 / 0:00

Diffusion and Effusion


Diffusion: mixing molecules of one gas with another as a result of random molecular movement. (This term is seen more in biology!)

Photo by CNS OpenStax / CC BY

PAGE BREAK
Effusion: Escape of gas molecules from their container through a tiny pinhole. This is what is important to us for gases!

Photo by CNS OpenStax / CC BY

According to the image above, do the green or purple particles have a faster rate of effusion?
Green

Wize Concept
A higher or faster rate of effusion means that those particles escape through the hole at a faster rate!

Do you think lighter or heavier molecules would be able to effuse faster?
Lighter!

PAGE BREAK

Graham's Law of Effusion:

rate of effusion Arate of effusion  B=(urms)A(urms)B=MBMA\boxed{\frac{\text{rate of effusion A}}{\text{rate of effusion }\ B}=\frac{\left(\text{u}_{\text{rms}}\right)_{\text{A}}}{\left(u_{\text{rms}}\right)_{\text{B}}}=\sqrt{\frac{\text{M}_{\text{B}}}{\text{M}_{\text{A}}}}}

where M=Molecular weight
A is for gas "A"
B is for gas "B"

Based on the equation, how is the rate of effusion for a particle related to its molecular weight? (directly proportional, inversely proportional, other, not related??)
inversely proportional to the square root of its molar mass

Practice: Graham's Law of Effusion

If we started with the same number of dark and light particles in one container and after 2 minutes we looked and saw that 4 dark particles and 2 light particles had effused to the other container, how much heavier/lighter are the dark particles than the light particles?


Practice: Speeds of Gases

An ambitious group of scientists conducted two separate experiments where they isolated 1000 atoms each of Li and Rb in a tiny volume of 5 x 10-15 m3 at a temperature of 1 Kelvin. How many times faster or slower would Li atoms be effusing than Rb atoms?
Extra Practice
Graham's Law: Effusion
An ambitious group of scientists conducted two separate experiments where they isolated 1000 atoms each of Li and Rb in a tiny volume of 5 x 10-15 m3 at a temperature of 1 Kelvin. How many times faster or slower would Li atoms be effusing than Rb atoms?
A mixture of Cl2 and Br2 is connected to an empty vessel with a small pinhole. After a long period of time has passed, what will be the ratio of Cl2 to Br2 particles present in the formerly evacuated vessel?
If it takes 24 minutes for a pressure of 20.0 kPa of fluorine gas to accumulate in a vessel through a pinhole, how long will it take for the same pressure to accumulate of H2 gas?
If a mixture of He and Xe are present in a vessel, and the root mean square speed of He is 412 m/s, what is the root mean square speed of Xe? What is the temperature of this vessel?
Nickel forms a gaseous compound of the formulaNi(CO)x{\small \text{Ni(CO)}_\text{x}}. What is the value of x given the fact that under the same conditions of temperature and pressure, methane(CH4){\small \text{(CH}_4)}effuses 3.3 times faster than the compound?
Effusion
One of two identical balloons contained carbon dioxide (CO2) gas and the other contained hydrogen (H2) gas. If it took 24 hours for all of the H2 to effuse out of its balloon, how long did it take for all of the CO2 to effuse?
Graham's Law: Kinetic Energy
1. If a mixture of He and Xe are present in a vessel, and the root mean square speed of He is 412 m/s, what is the root mean square speed of Xe? What is the temperature of this vessel?
Graham's Law
2. If it takes 24 minutes for a pressure of 20.0 kPa of fluorine gas to accumulate in a vessel through a pinhole, how long will it take for the same pressure to accumulate of H2 gas?
Graham's Law
4. A mixture of Cl2 and Br2 is connected to an empty vessel with a small pinhole. After a long period of time has passed, what will be the ratio of Cl2 to Br2 particles present in the formerly evacuated vessel?
Gas Laws: Diffusion & Effusion
In the above example, if we started with the same # of dark and light particles and after a certain amount of time passed we looked and saw that there were 4 dark particles and 2 light particles, how much heavier/lighter are the dark particles than the light particles?
If it takes 22.0 minutes for a pressure of 34.0 kPa of neon gas to accumulate in a vessel through a pinhole, how long will it take for the same pressure to accumulate of H2 gas?
Graham's Law
Two gas vessels are linked by a small pinhole which can be opened or closed. When one vessel is evacuated and the other is charged with 100 kPa of F2 gas, it is found that a pressure of 7.42 kPa accumulates in the evacuated vessel after the pinhole has been opened for 15 minutes. If the same experiment was repeated with Cl2 gas, what would the pressure in the evacuated vessel be after 15 minutes? Report your answer in kPa to two decimal places.
A mixture of Cl2 and I2 is connected to an evacuated (empty) vessel with a small pinhole. After an hour has passed, the pin hole is closed. What will be the ratio of Cl2 to I2 particles present in the formerly evacuated vessel?
Effusion
In an effusion experiment, 5.52⋅10−35.52\cdot10^{-3} mols Cl2 was found to effuse through a little orifice in 82 seconds. In another experiment, 4.32⋅10−34.32\cdot10^{-3} mols of an unknown gas effused out under same experimental condition in 47 seconds. Identify the unknown gas.
Graham's Law: Effusion
An ambitious group of scientists conducted two separate experiments where they isolated 1000 atoms each of Li and Rb in a tiny volume of 5 x 10-15 m3 at a temperature of 1 Kelvin. How many times faster or slower would Li atoms be effusing than Rb atoms?