Effusion and Real Gases

Review: Kinetic Molecular Theory of Gases

Which of the following is true?

• The average speed of gas molecules decreases with decreasing temperature.

• The kinetic energy of a molecule cannot determine its speed.

• There are gas molecules that move slower than the average.

• All the gas molecules in a sample cannot have the same kinetic energy.

• The average kinetic energy of gas molecules decreases with decreasing temperature.

Effusion: Process of escaping through tiny holes, (often into an empty container, although not always).

Diffusion: Movement of molecules (typically in liquid or gas) from area of high to low concentration through larger openings.

For each circumstance say if the gas is effusing, diffusing or neither:Picture A)

Picture B)

Movement of helium particles through a balloon causing it to deflate over time.

Movement of helium particles into the air when the mouth of a balloon is opened.

Enriching isotopes by using the difference in rms speeds to separate different mass molecules.

Perfume molecules spread from a spay on one side of the room to the other.

A)

B)

For an Oxygen and Bromine gas mixture which molecules have the larger:

• Mass?

• Greatest average velocity?

• Rate of effusion?

• Partial Pressure?

• Average kinetic energy?

CONCEPT: KINETIC MOLECULAR THEORY EFFUSION:

• Without doing any calculations, put the following in order of increasing rate of effusion and time of effusion. Molecular masses are in parenthesis.

• Ne (20.18 g/mol), C3H8 (44.11), He (4.00) and NO2 (46.01)high mass equals slow (aka low rate, long time): low mass equals fast (aka high rate, short time)

CALCULATIONS: KINETIC MOLECULAR THEORY

• What is the molar mass of a compound that takes 2.7 times as long to

effuse through a porous plug as it did for the same amount of XeF2 at

the same temperature and pressure?

Hint:

Real vs. Ideal Gas

• Under what types of pressure do gases behave ideally?

• Under what type of temperatures do gases behave ideally?

• We originally defined ideal gases with as series of requirements. These included, no volume, elastic collisions, and they do not interact. Match these requirements with the conditions above.

• We haven’t learned about how to tell if molecules interact with each other yet (it is in 1B), however, would a molecule that strongly interacts with other molecules be more or less ideal?

REAL GAS EXAMPLE (we may not have time for this one the

real gas material, depending on the speed of the class we may finish this up on

Friday.)

• Calculate the pressure exerted by 1.00 mol of C2H6 behaving

as an ideal gas and a Van der Waals gas when it is at 1) 273.15K in 22.414L and also 2) at 1000. K in 0.100L. Think about what these answers tell you.

Ideal Gas Law

Van Der Waals Gas

Conditions 1a=4.562b=0.0638

REAL GAS EXAMPLE (we may not have time for this one the

real gas material, depending on the speed of the class we may finish this up on

Friday.)

• Calculate the pressure exerted by 1.00 mol of C2H6

behaving as an ideal gas and a Van der Waals gas when it is at 1) 273.15 in 22.414L and also 2) at 1000. K in 0.100L. Think about what these answers tell you.

Ideal Gas Law

Van Der Waals Gas

Conditions 2

REAL GAS EXAMPLE (we may not have time for this one the

real gas material, depending on the speed of the class we may finish this up on

Friday.)

• Calculate the pressure exerted by 1.00 mol of C2H6

behaving as an ideal gas and a Van der Waals gas when it is at 1) 273.15 in 22.414L and also 2) at 1000. K in 0.100L. Think about what these answers tell you.

Ideal Gas Law

Van Der Waals Gas

Summary

Difference 0.006atm 989atm

Condition 1Atmospheric like

Condition 2High Pressure