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Mathematics Clinic => Grade 9 Mathematics => Topic started by: clippers! on Oct 4, 2013

Title: Is there any tricks to knowing which gas law or gas equation to use when you are reading a chemistry word prob?
Post by: clippers! on Oct 4, 2013

I don't understand, when I'm reading a chemistry word problem, which formula I'm supposed to use.  I think I have the equations down if I know which equation to plug the numbers into.  I have a quiz tomorrow and we just finished up the chapter yesterday.  Any suggestions.  Anything would be appreciated.  Thanks

Title: Is there any tricks to knowing which gas law or gas equation to use when you are reading a chemistry word prob?
Post by: curlz on Oct 4, 2013

I think it's good to just remember: PV = nRT

so if the # of moles is constant and you know that R is the ideal gas constant then simply rearranging the equation algebraically gives:

PV/T = constant

and if any of the properties are not given in your word problem, then you can simply take it out of the equation and continue with the properties you are given.

For example, if a question only involves P and V, then your equation of interest will be PV = constant & if a question involves V and T, then ur eqn becomes: V/T = constant etc

Goodluck

Title: Is there any tricks to knowing which gas law or gas equation to use when you are reading a chemistry word prob?
Post by: Yolanda on Oct 4, 2013

remember PV = nRT

then remember this...

1) whatever is constant, move to the right.  the rest move to the left....
2) make 2 conditions 1 and 2.. and make the variable part of the equations =... like this..

PV = nRT..
if V is constant and n is constant (which is usually the case) and R is constant. then...

P/T = nR/V.... the right side is all constants...
P1 /T1 = nR/V
P2 / T2 = nR/V
so
P1 / T1 = P2 / T2  
same for P, n and R being constants...

PV = nRT
V / T = nR/P
V1 / T1 = V2 / T2

etc...

************************
alternately, and this is what I recommend... R is always constant... so

PV = nRT
PV / nT = R...
ie...

(P1V1) / (n1 T1) = (P2 V2 / n2 T2).... if you remember this equation and you cancel out whatever is constant, you should have no problems.  ok?  and fyi, the easy way to remember this equation is... PV = nRT.... PV/nT = R = constant...P1V1/n1T1 = ...

so memorize...

PV = nRT and
(P1V1) / (n1 T1) = (P2 V2 / n2 T2)....