View Full Version : Chemistry gas laws prediction?

Foobarz

October 6th, 2011, 02:33 AM

Ok so according to Avogadro's law, number of moles is directly proportional to volume. (n1/v1)=(n2/v2). Does that mean since volume is indirectly proportional to presssure (p1v1=p2v2), that number of moles is proportional to pressure? AKA (n1/p1=n2/p2)? Is that correct?

sffvba[e0rt

October 6th, 2011, 02:38 AM

Sounds right to me...

404

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Smilax

October 6th, 2011, 02:53 AM

Ok so according to Avogadro's law, number of moles is directly proportional to volume. (n1/v1)=(n2/v2). Does that mean since volume is indirectly proportional to presssure (p1v1=p2v2), that number of moles is proportional to pressure? AKA (n1/p1=n2/p2)? Is that correct?

pV = nRT

number of moles is directly proportional to volume

at a constant pressure, temperature

number of moles is proportional to pressure

at a constant volume, temperature

pV = nRT

ninjaaron

October 6th, 2011, 02:54 AM

Sounds like homework.

Smilax

October 6th, 2011, 02:58 AM

well yea, but, he did give the answer himself, so

it's more a discussion than a 'free answer'

tgalati4

October 6th, 2011, 04:58 AM

The perfect gas law is quite handy. You can use it to design speaker boxes to estimating air conditioning requirements by mixing air from two rooms.

http://en.wikipedia.org/wiki/Perfect_Gas_Law

It's not homework if it's interesting.

beew

October 6th, 2011, 05:40 AM

Smilax is absolutely right, OP needs to specify the conditions constant temperature and constant pressure for the statement that number of moles is proportional to volume to make sense.

@Op

The ideal gas law only works approximately, it works better when density of gas is low (N/V is small) and temperature is high. That way interactions between gas molecules and kinetic energy of their internal degrees of freedom (vibration and rotation for example) can be neglected so that the molecules can be treated as hard spheres which only interact through collisions.

vrhahaha

October 6th, 2011, 06:27 AM

i don't know much about chemistry. but given equation (n1/v1)=(n2/v2) and (p1v1=p2v2), the result is n1p1=n2p2 instead of n1/p1=n2/p2.

Smilax

October 6th, 2011, 05:51 PM

i don't know much about chemistry. but given equation (n1/v1)=(n2/v2) and (p1v1=p2v2), the result is n1p1=n2p2 instead of n1/p1=n2/p2.

maybe you should look again

vrhahaha

October 8th, 2011, 03:41 PM

maybe you should look again

Can you please enlighten me? I don't know what went wrong with my arithmetics, several tries give me the same answer

thatguruguy

October 8th, 2011, 03:53 PM

i don't know much about chemistry.

I don't know much about history (http://www.youtube.com/watch?v=VF6JMotbHYM).

Smilax

October 26th, 2011, 12:36 PM

Can you please enlighten me? I don't know what went wrong with my arithmetics, several tries give me the same answer

for this equation to be valid.

(n1/v1)=(n2/v2)

it's required to specify that the pressure and temperature are held constant.

for this equation to be valid

p1v1=p2v2

it's required to specify that the number of moles and temperature are held constant.

i think the problem you where having is tring to substitute an expression with the number of moles (n) as a variable into an equation where the number of moles is a constant.

why is number of moles a constant in one and not the other, because it was defined as a constant, if it wasn't defined as a constant it would still be in both equations.

if you care to try again start with the equation PV = nRT.

as such....

PV = nRT

holding V,olume and temperture constant we see,

p is proportional to n

or

Cp1 = n1 where C is some constant

and Cp2 = n2

dividing

Cp1/Cp2 = n1/n2

which gives n1/p1 = n2/p2

kind regards.

smilax

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