steven2984
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Effusion!!! I need help!
yes, its me once more! I need some help from my fellow chem geniuses. This is the prob. that has me stuck:
The effusion rate of an unknown gas is measured and found to be 31.50 mL/min. Under identical expermential conditions, the effusion rate of O2(oxygen)
is found to 30.50 mL/min. If the choices are CH4, CO, NO, CO2, and NO2, what is the indentity of the unknown gas?
My book says the answer is NO. but i dont see how the answer is obtain. what steps and equation are used???
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steven2984
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disregard this post
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solo
International Hazard
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Registered: 9-12-2002
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Mood: ....getting old and drowning in a sea of knowledge
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I hope this review will help you,
" The effusion of a gas is its movement through an extremely tiny opening into a region of lower pressure. The term diffusion really
only speaks to the direction of gas movement. Effusion speaks for not only the direction but the rate that a change occurs.
An English scienetist, Thomas Graham (1805-1869), studied the rates at which various gases effuse, and he found that the more dense the gas
is, the slower it effuses. The exact relationship between rate and gas density, d, is called Graham's Law of Effusion.
(effusion rate)A X (dA)1/2 = (effusion rate)B X (dB)1/2
Finding the densities of gases at various temperatures is often difficult to do. With a little chemical slight of hand we can get a formula
for a much simpler answer.
(effusion rate)A X (molecular massA)1/2 = (effusion rate)B X (molecular massB)1/2
Example: Under the same conditions of temperature and pressure, does hydrogen iodide or ammonia effuse faster? Calculate the relative rates at
which they effuse.
molecular mass of HI = 128 molecular mass of NH3 = 17.04
( effusion rate of NH3 ) X (17.04)1/2 = ( effusion rate of HI ) X (127.91)1/2
This rearranges to rate for NH3 = (127.91)1/2
rate for HI (17.01)1/2
This rearrange into rate for NH3 = (127.91/17.01)1/2
rate for HI
= 2.74
Thus ammonia effuses almost three times as fast as hydrogen iodide.
As a general rule the more a molecule masses the slower it moves. To find a mathematical value to this rate use Graham's Law. "
So with that in mind one can make a choice of NO tobe your mystery compound gas......
source,http://www.ucdsb.on.ca/tiss/stretton/chem1/gases7.html
Saludos, from Latin America
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