Graham's law
-
Upload
roxanne-elysse-bunayog -
Category
Documents
-
view
897 -
download
3
Transcript of Graham's law
Graham's LawDiffusion and Effusion
Din | Ramil | Santos | Luna |
Inton | Bunayog
Motivation
! To be able to understand the basic principles of Graham's Law.
To analyse the difference of diffusion from
effusion
To define diffusion
and effusion
To identify the
applications of Graham's
Law
checklist(Objectives)
Let’s start the discussion
Gases (Short)Kinetic Molecular Theory
DiffusionEffusion
Thomas GrahamGraham’s Law
Before we start
Before we start
We would like to point out that we strongly disagree with this* and you should too.
*Only from this point and until this report ends :D
gases
Topic: Just Gas
Topic: Just Gas
The entire space in which molecules of a gas move represents the volume of the
gas.
» Moles of gases are always in rapid, random, straight line motion, endlessly bumping against each other and
hitting the walls of the container. This is discussed in the Kinetic
Molecular Theory.
Topic: Kinetic molecular Theory
Topic: Kinetic molecular Theory
Kinetic Molecular TheoryGases are very far from each
other.
There are no interaction (attraction) between the
molecules.
They collide with each other and with the walls of the
container in a perfectly elastic manner.
Diffusion
Topic: Diffusion
»The rate at which two gases mix; movement of gases from high
concentration to low concentration; mixing of gases due to molecular
motion
Topic: Diffusion
Topic: Effusion
» movement of gases from high pressure to low
pressure
Topic: Effusion
Effusion
Topic: Diffusion and Effusion
» Diffusion
is the process of
slowly mixing
two gases together.
Topic: Diffusion and Effusion
Diffusion % Effusion
» Effusion is the process that occurs when a gas is permitted to escape its
container through a
small opening.
Topic: Diffusion and Effusion
» Diffusion movement of gases
from high concentratio
n to low concentratio
n
Topic: Diffusion and Effusion
Diffusion % Effusion
» Effusion movement of gases from
high pressure to
low pressure
Topic: Thomas Graham
Topic: Thomas Graham
Thomas graham
He formulated the law of diffusion. Also
called Graham’s Law in 1846.
» 1805-1869» Scottish chemist
Topic: Graham’s Law
Topic: Graham’s Law
Graham’s law of diffusion
"The velocity of a gas at a certain temperature is inversely proportional
to the square root of its molecular mass."
Topic: Graham’s Law
Topic: Graham’s Law
Graham’s law of diffusion
Graham's law is a gas law which relates the rate of diffusion or effusion of a gas to its molar
mass.This means light gasses effuse or diffuse quickly and heavier gases
effuse or diffuse slowly.
Topic: Graham’s Law
Topic: Graham’s Law
Graham’s law of diffusionThis means light gasses effuse or diffuse
quickly and heavier gases effuse or diffuse slowly.
Hydrogen Helium
Helium is lighter than Hydrogen
Topic: Graham’s Law
Topic: Graham’s Law
Graham’s law of diffusionThis gas law is derived directly from the kinetic molecular theory. Consider two gas molecules:
Each gas molecule has its corresponding mass, m, and volume, v. If they are at the same absolute temperature,
then their kinetic energies are equal.
a B
Topic: Graham’s Law
Topic: Graham’s Law
Graham’s law of diffusionEach gas molecule has its corresponding mass, m, and
volume, v. If they are at the same absolute temperature, then their kinetic energies are equal.
Topic: Graham’s Law
Topic: Graham’s Law
Graham’s law of diffusionThe mass can be related to the molecular weight of the
gas
"The velocity of a gas at a certain temperature is inversely proportional
to the square root of its molecular mass."
Topic: Graham’s Law
Topic: Graham’s Law
Graham’s law of diffusionThe mass can be related to the molecular weight of the
gas
Gases with high molecular weight tend to diffuse more slowly than gases with low molecular weight
Higher molecular weight : NumeratorLower molecular weight : Denominator
Higher velocity: NumeratorLower velocity: Denominator
let’s try it out
?
Sample Problem
How much faster does O2 escape through a porous container than SO2?
(Use the periodic table to get the molecular weight of gas)
Sample problem
MWO2 = 32.0 g/molMWSO2 = 64.0 g/mol
Solution:Substituting these
values in theEquation for Graham’s
law of diffusion.
MWSO2
MWO2VSO2
VO2
VSO2
VO2 64 g/mol
32 g/mol=
=8
5.66VSO2
VO2
Given:
Sample Problem
How much faster does O2 escape through a porous container than SO2?
(Use the periodic table to get the molecular weight of gas)
Sample problem
Final answer:This means that O2 diffuses 1.41 times as
fast as SO2.
=8
5.66VSO2
1.41=VSO2
VO2
VO2 = 1.41
Solution:
VSO2
VO2
VO2 = 1.41 VSO2
applications
APPLICATIONS
APPLICATIONS
1. When someone sautés meat with garlic and onion, the volatile substances responsible for the
aroma of the spices vaporize and mix with the gases in the air.
APPLICATIONS
APPLICATIONS
2. A balloon filled with air and a boy allows the gas to escape, the gas molecules will diffuse among the
molecules of air and mixture of gases will occupy the whole room. Thus, we say that a gas spreads throughout
the space available to it.
Quiz
Ready?
quiz
Quiz
1. How much faster does O2 escape through a porous medium than CO2
given the same conditions?
2. Determine how much faster He would escape through a porous medium than N2
under the same conditions.
Answers
Ready?
VCO2
Answers
Answers
1. How much faster does O2 escape through a porous medium than CO2 given
the same conditions?
MWCO2
MWO2VCO2
VO2
VCO2
VO2 44 g/mol
32 g/mol=
=6.63 (6.6332)
5.66 (5.6568)VCO2
VO2
1.17=VCO2
VO2
=VO2 =
1.17MWO2 = 32.0 g/molMWCO2 = 44.0 g/mol
Solution:
Given: Final answer:
VCO2
Answers
Answers
2. Determine how much faster He would escape through a porous medium than N2
under the same conditions.
MWN2
MWHeVN2
VHe
VN2
VHe 28 g/mol
4 g/mol=
=5.29
2VN2
VHe
2.65 VN2=VN2
VHe
= 2.65 VN2VHe MWN2 = 28.0 g/molMWCO2 = 4.0 g/mol
Solution:
Given: Final answer: