Diffusion and Effusion

Graham's Law of Effusion

Mrs. Nebzydoski

Diffusion vs Effusion

Diffusion is when gases move throughout a space to reach an equilibrium.

Effusion is a gas escaping through a small hole.

Size matters:

• Small gas particles travel faster than large gas particles

• Small molecules effuse faster thsn larger molecules

Multiple Choice

Which will travel faster: oxygen gas or helium gas?

• O₂

• He

Multiple Choice

Which travels faster? CO₂ or Ar?

• CO₂

• Ar

Equation:

The speed at which a gas effuses is dependent upon the size of the molecule.

Solving the equation:

We usual make gas B the BIGGER gas and gas A the smaller gas for calculations.

Example:

How much faster does hydrogen gas travel than neon gas?

Than answer is 3 x faster....

Multiple Choice

How much faster will He(g) travel than O₂(g)?

• 4 times faster

• 2.8 times faster

• 0.35 times faster

• 0.125 times faster

How to work out the last question...

Try this one on paper....

If an unknown gas travels 3 times faster than neon gas , what is the molar mass of the gas?

Multiple Choice

your answer to the problem you wrote down from the previous slide?

• 1.1 g/mol

• 2 g/mol

• 0.15 g/mol

• 0.45 g/mol

How to solve the last problem

Multiple Choice

Usuing Graham's Law: If you had 2 identical balloons filled with Nitrogen gas (N₂) and Helium gas (He), which balloon will deflate the fastest?

• Helium balloon

• nitrogen balloon

• they will both deflate at the same rate

• the balloons will both pop

Multiple Choice

What is the chemical formula for the white solid "cloud" made in the reaction you just saw?

• ammonia

• hydrochloric acid

• ammonium chloride

Multiple Choice

Did the ammonium chloride cloud form closer to the NH₃ side or the HCl side of the tube?

• NH₃

• HCl

Open Ended

Using Graham's Law: Explain why the cloud of ammonium chloride formed closer to the ammonia side of the tube than the hydrochloric acid side of the tube.