Graham's Law

The rate of effusion of water vapor is 0.391 and the rate of effusion of propane is 0.251 at the same temperature and pressure.  What is the molar mass of propane? (write the formula and show your work)

• 44.0 g/mol

• 6.63 g/mol

• 0.37 g/mol

• 28.2 g/mol

Effusion and diffusion rates are inversely proportional to the square root of the molar mass of the gas.

• True

• False

Which of the following gases will effuse most slowly under the same physical conditions?
Don't forget to check for diatomics!

• Hydrogen

• Chlorine

• Ammonia (NH₃)

• Bromine

Which will travel faster: oxygen gas or helium gas?

• O₂

• He

An unknown gas diffuses 0.25 times as fast as He (4 g/mol). What is the molecular mass of the unknown gas?

• 128

• 64

• 32

• 16

Effusion is

• used to describe the combustibility of a gas.

• ability of a gas to escape through a tiny opening

• what occurs after diffusion.

• the ability of a gas to mix with other gases.

why would O₂ effuse faster than CO₂ in the same room

• because O₂ has more energy

• because CO₂ has a greater molar mass

• because oxygen has a higher temperature

• they will effuse the same because the temperature is fixed

Heavier gases have a __________________ rate of effusion.

• Faster

• Slower

• Rate of effusion does not depend on mass.

According to Graham's Law, the rate of effusion of a gas is inversely proportional to the square root of its molar mass. If Gas A has a molar mass of 4 g/mol and Gas B has a molar mass of 64 g/mol, which gas will effuse faster and by what factor?

• Gas A will effuse 4 times faster than Gas B

• Gas B will effuse 4 times faster than Gas A

• Gas A will effuse 2 times faster than Gas B

• Gas B will effuse 2 times faster than Gas A

If the rate of effusion of hydrogen gas is 4 times that of an unknown gas, what is the molar mass of the unknown gas?

• 16 g/mol

• 32 g/mol

• 64 g/mol

• 128 g/mol