There is one formula and you CAN get the same answer no matter which formula is used. It is PV = nRT; however, some problems don't list the moles (just P, V, and T for one set of conditions and something for another set of conditions). Therefore, to use the one formula one must solve PV = nRT for the first set of conditions, find n, then use that n with the second set of conditions and PV = nRT to find whatever the unknown is. And there is nothing wrong with that but some of us are lazy and we use (P1V1/T1) = P2V2/T2) as a shortcut which gets the correct answer with just one calculator manipulation. And those are the only two equations you need to know.
1. PV = nRT when you need to calculate n and
2. (P1V1/T1) = (P2V2/T2) when you want to take the shortcut and have the information to do so.
But what about P1V1 = P2V2 and P1/T1 = P2/T2 and V1/T1 = V2/T2 you say? Those are NOT separate formulas; they all come from (P1V2/T1) = (P2V2/T2).
Here is what you do.
If the problem lists P and V with one set and it gives P and asks for V for another set, just mentally cover up the T1 and T2 in that #2 equation. That gives you P1V1 = P2V2 and solve the unknown. Or if the problem gives a V1 and V2 and T2 and asks for T1, just cover up the P1 and P2 mentally and you have V1/T1 = V2/T2 and solve for the unknown. You get the idea. I hope this helps. It CAN be confusing but it need not be if you just remember those two and make your own for what you need.
Can someone please explain why there are so many gas laws. I've been doing my homework with the appropriate formulas, but I'm confused why everyone keeps say that PV=nRT is so wonderful? You can't get the same solution by using this ONE formula, so what is so wonderful?
Is there ONE formula or must I pay close attention to the constants in the word problem?
Thanks for your help!!!
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