If the volume of a gas container at 32.0 Solution anytime you get a gas problem
ID: 616382 • Letter: I
Question
If the volume of a gas container at 32.0Explanation / Answer
anytime you get a gas problem like this use this equation... P1V1 / (n1T1) = P2V2 / (n2T2) in this case...T and V are free to vary.... n and P are constant...so n1 = n2 and P1 = P2... so we can cancel them out..and... P1V1 / (n1T1) = P2V2 / (n2T2) becomes V1 / T1 = V2 / T2 rearranging and solving... T2 = T1 x (V2 / V1) T2 = 305 K x (0.755 L / 1.55 L) = 149 K = -124 C **************** notes... 1) P1V1 / (n1T1)... came from PV = nRT ---> PV/nT = R = a constant meaning any PV / nT = any other PV / nt 2) hardest part of this is determining what is constant. n and P. this takes practice. 3) I converted 32.0 C to K.. you must ALWAYS use K or R. never C or F 4) watch the units on volume. 755 mL = 0.755 L... same units as 1.55 L ********* fyi.. in my experience, having worked with thousands of students on this topic, people spend more time and make more mistakes trying to remember gas laws, which one they should apply, setting up the "proportions", and solving them than they do via the process I showed you here. seriously.. Shashiketan's answer is a perfect example. Shashiketan wrote... VT= const. [charles law] 1.55*(32+273)=(0.755*x) Shashiketan should have written.. V / T = a constant 1.55 / (32+273)=(0.755 / x) x = 0.755 / 1.55 x (32 + 273)... and of course, I absolutely require units to be carried along but that wouldn't have helped much in this case.. *************** The process I showed you involves memorizing 1 equation. PV = nRT. Then learning to manipulate it into PV / nT = R. then P1V1 / (n1T1) = P2V2 / (n2T2). And then you need to recognize what varies and is constant. Which you need for either process. one other thing. what happens if you get a problem like let's say you have a tank of air with a valve. The valve is opened. After a time the temp has dropped from 30 C to 20 C. The pressure has dropped from 3000 psi to 1500 psi. What % of O2 is left in the tank? which equation do you use?