Question

A 3.80 L cylinder contains 6.83 g of methane, CH4, at a pressure of 3320 mmHg. What is the temp. Of the gas?

I mainly have problems being able to tell which gas law equation I need to use when asked these types of questions and then being able to rearrange the equation to find my answer that I need. If there an easy way to do this or to be able to tell?
Thank you.

Answer 1

If you have two sets of conditions, the easy gas law to use is the
(P1V1/T1) = (P2V2/T2)

If you don't have two sets of data you almost certainly must use PV = nRT. Many times, and this problem is one of them, the problem gives grams so you calculate mols = n = grams/molar mass.

Also,if you mean by "rearranging the equation to find my answer" as rearranging the equation FIRST, I wouldn't do that. I would substitute into the equation you want (either of the two equations above), then rearrange the numbers to solve for the unknown.
For this problem you want PV = nRT.
P must be in atm (mmHg/760), n = mols = grams/molar mass, when you solve for T the answer will be in kelvin.