What is the effusion rate of hydrogen iodide?

Question

Under the same conditions of temperature and pressure, does hydrogen iodide (HI) or

ammonia (NH3) effuse faster? Calculate the relative rates at which they effuse.

Ps. The effusion rate of ammonia is approximately 2.74, right? How about hydrogen iodide?

Answer 1

The effusion rate of a gas is inversely proportional to its molar mass. Thus, the heavier the gas, the slower the effusion rate.

Comparing HI to NH3 we have the following molar masses:

HI = 128 g/mol

NH₃ = 17 g/mol

So, NH₃ will effuse faster

Graham's Law relates the rate of effusion to the molar mass as follows:

rate gas 1/rate gas 2 = sqrt MW gas2/sqrt MW gas 1

For HI and NH3 we would have the following relationship:

2.74/x = sqrt (128/17)

2.74/x = 2.74

x = 1

So, HI would effuse at a rate of 1.00 (HI effuses 2.74 x faster)