Re: Chemistry Question help

That is correct, although it is based on the assumption that you are 
dealing with theoretical "ideal gases", for which the ideal-gas 
equation  PV = nRT applies.



For gases under conditions of P and T that are not far from 
liquefaction, you would need to use a more complicated equation of state
 that takes account the space occupied by molecules and intermolecular 
attractions, in particular the Van Der Waals' equation, which has to be 
solved as a cubic equation. Alternatively, one could use empirical 
"compressibility factors", z, for a modified ideal-gas law PV = znRT. 
These are tabulated for various gases at various temperatures and 
pressures at ratios of their critical temperatures and pressures, and 
solved for the other variable using a graph or gnomon. These methods are
 described at length in Perry's Chemical Engineers' Handbook.



While it is true that the diffusivities of gases vary inversely as the 
square root of their molecular (or atomic) weights, they are also 
strongly influenced by the gases' atomicity (and hence molecular size) 
and intermolecular attraction. For this reason, the diffusivity of Ne 
(atomic weight 20), a monatomic inert gas with very little 
intermolecular attraction due to lack of polarity, cannot really be 
compared with that of CO (molecular weight 28), a diatomic gas with a 
strongly polar multiple C=O bond and hence substantial intermolecular 
attraction (and as the result a much higher melting/sublimation point at
 the same pressure), simply on the basis of molecular weights. The 
molecular size of Ne is smaller than that of CO, and in fact is smaller 
than even that of the isoelectronic F- anion due to the greater nuclear 
charge. The diffusivity of Ne would therefore be much higher than that 
expected simply by comparison of its molecular weight with that of CO. 
This is also discussed at length in Perry's Chemical Engineers' 
Handbook, which gives a semiempirical equation for gas diffusivities.



John W.

--- On Thu, 17/11/11, Saim Rauf <[email protected]> wrote:
From: Saim Rauf <[email protected]>
Subject: Re: [The Chemistry Cluster] Chemistry Question help
To: "[email protected]" <[email protected]>
Date: Thursday, 17, November, 2011, 8:55 PM








 



  


    
      
      
      



for your problem no. 1 the equation to use is of boyle's law which is



P.V=P'.V'   (if the temp. remains constant)



for problem no . 2 the equation to be used is



V / T=V'/T'      (where the temp. is taken in kelvins)



for problem no. 3 we use   boyles and charles law combined as



(P.V)/T = (P'.V')/T' (the temp is measure in kelvins)



and since the vol. is constant it can be dropped from both sides.



as regarding prob no. 4... as we know the volume of gas directly varies with the no. of moles so we use equation



V/n=V'/n' (where n'=no of moles present + added no of moles)



for your fifth problem ideal gas equation is to be used as



(P.V)/T = (P'.V')/T'



the sixth problem is quite easy... we have to use daltons law of partial pressures according to which



total pressure = pressure exerted by first gas + pressure exerted by second gas + pressure exerted by third gas + ............



and now your seventh problem.. the molar mass of neon is 20 where as the
 molar mass of CO is 12+16=28 thus by grahams law of effusion... we have



rate of effusion of gas 1 / rate of effusion of gas 2 = sqrt(molar mass 
of gas                                                                  
                1)/ sqrt(molar mass                                      
                                                             of gas 2)

so the rate of effusion of a gas inversely varies with its molar mass 
thus we infer the rate of effusion of neon is more than that of CO.. 
(the same solution holds for diffusion)..



REGARDS



________________________________

From: smileyranger_iie <[email protected]>

To: [email protected]

Sent: Tuesday, November 15, 2011 6:29 PM

Subject: [The Chemistry Cluster] Chemistry Question help



  

Cn you guys please help me with the following questions? 



At constant temperature, a gas occupies a volume of 840 mL at 520 mm Hg.
 If we increase the pressure to 705 mm Hg, what will be the volume of 
the gas?



At constant pressure, a gas occupies a volume of 270 mL at 320 C. What is the volume of the gas at -210 C?



We have 950 mL of a gas at 200	C and 350 mm Hg.	If we heat the gas to 1750	C at constant volume, what will the pressure be?



A balloon holding 390 mL holds 2.8 moles of argon. If we add 3.2 moles 
of the gas at the same temperature and pressure, what will the volume of
 the balloon be?



You have 540 mL of a gas at a pressure of 723 mm Hg and a temperature of
 340 C. What is the volume if you change the pressure to 840 mm Hg and 
the temperature to 91 0C?



A mixture of three gases is in a container. The mixture exerts a total 
pressure of 456 atmospheres. If gas A exerts a pressure of 195 
atmospheres and gas B exerts a pressure of 97 atmospheres, what is the 
pressure of gas C?



Which gas will diffuse faster: Ne or carbon monoxide (CO)? Explain your answer.



Thanks!



-Smileyranger :3





[Non-text portions of this message have been removed]



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