HELP... Chem final GAS LAWS

[crazytonurse]

I have my Chem Final tomorrow and I know that the Gas laws will be on it.. I hate them and I have no clue how to figure out which law to use when. Anyone here have any advice? PLEASE :eek::eek:

[tfleuter, BSN, RN]

Ok, if I remember correctly: Follow the constants!! You will deal with 3 factors: Temp (T) Pressure (P) and Volume (V). Whatever the constant is, it will not be included in the equation, or simply state that something remains the same before and after. Temp always goes in denominator of the "fractions" so that will help keep things in place. Examples:

If the constant is Temperature, then it is Boyle's law. Boyle sounds like "boil" which has to do with temp. So the equation goes

(P1)(V1) = (P2)(V2)

P1 = pressure before, P2 = pressure after, same with "V". Which ever variable you are asked to solve for is "x"

If the constant is Pressure, it is Charles's Law. I remember this one by thinking "Charlie's Angels put pressure on the bad guys" I know, I know, dorky as can be, but it worked!! The equation then leaves you with Temp and Volume and since temp always goes on bottom, volume must go on top:

V1 = V2

T1 T2

If volume is the constant, then it is Gay Lussac's Law. The "L" in the name and the "V" for volume made me think of Luis Vuitton which for whatever reason helped me link back to the name (again, I have a weird mind). Temp always goes on bottom, so pressure on top:

P1 = P2

T1 T2

Now, if you are given all three factors, you can probably assume that you need to use the Combined Gas Law, which again, temp always goes on bottom:

(P1)(V1) = (P2)(V2)

T1 T2

Finally, if you are given a combination of Temp, Volume and Pressure in addition to the AMOUNT of a substance (whether it be in grams or Moles) then you can assume that you will need to use the Universal Gas Law which is PV=nRT. Whenever I suspected I had this type of problem I would set up the following:

P=__

V=__

n=__

R=__

T=__

Which ever piece of information the problem did not give let me know what I needed to solve for. If I wasn't give pressure, then I knew I needed to figure out P =

nRT

V

If I needed to find moles then n=

PV

RT

Anyways, I hope this helps at all! It's what worked for me

[coffeeaftermidnight]

To remember temp goes on the bottom, I visualized the T as a bunsen burner. ha ha!

[crazytonurse]

Thank you so much! I got my grade for the final and I got a 93% the majority of the class bombed it. Thanks to the final I have an A for the course! :)

[tfleuter, BSN, RN]

Congrats!