Chemistry Questions

Question

Which of the following gases effuses most rapidly?

Select one:

a. Carbon monoxide

b. Oxygen

c. Nitrogen

d. Ammonia

e. Hydrogen chloride

Arrange the following gases in order of increasing rate of effusion.

C₂H₆     Ar          HCl       PH₃

Select one:

a.C₂H₆ < HCl < PH₃ < Ar

b.Ar < HCl < PH₃ < C₂H₆

c.Ar < PH₃< HCl < C₂H₆

d.C₂H₆ < PH₃ < HCl < Ar

e.Ar < PH₃ < C₂H₆ < HCl

Which of the following changes will not affect the total pressure of gas in a container, assuming all other factors remain constant?

Select one:

a. The temperature of the sample is altered.

b. Half of the molecules are replaced by an equal number of molecules of a gas with a different molecular weight.

c. The total number of molecules is altered.

d. The frequency of collisions of molecules with the walls is increased.

e. The average velocity of the molecules is lowered.

Answer 1

Look up and read about Graham's Law of Effusion.

The rate of effusion of a gas is inversely proportional to the molar mass of the gas, ie heavier gases effuse more slowly and lighter gases effuse more rapidly.

a. Carbon monoxide MW = 30 g/mol

b. Oxygen MW = 32 g/mol

c. Nitrogen MW = 28 g/mol

d. Ammonia MW = 17 g/mol

e. Hydrogen chloride MW = 37 g/mol

Ammonia will effuse most rapidly as it is the lightest.

C₂H₆ MW = 30 g/mol

Ar   MW = 40 g/mol      

HCl  MW = 37 g/mol      

PH₃ MW = 34 g/mol

In order of increasing rates of effusion we have...

C₂H₆ < PH₃ < HCl < Ar (ANSWER d)

b. Half of the molecules are replaced by an equal number of molecules of a gas with a different molecular weight.