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: