Asked by Katy

A sample of helium behaves as an ideal gas as it is heated at constant pressure from 273 K to 373 K. If 15.0 J of work is done by the gas during this process, what is the mass of helium present?


I am not sure what equations to use for this problem....
Answered by Damon
PV=nRT
p dV + V dp = n R dT
p is constant here so
p dV = n R dT
work = integral p dV = nR dT
p(V2-V1) = n R (T2-T1)

so 15 = n R (T2-T1)

Answered by Katy
doesnt that give me an answer in moles? ...is there a way to convert moles to mg?
Answered by Katy
so i got the answer to be .01804 moles

and i know one mole of helium is 4.03 g


do i just multiply the two together? and then divide by 10000 to convert g to mg?
Answered by Katy
never mind. I made a silly error.

i got .01804 moles...multiplied that times 4.03grams and then multiplied that times 1000 and got 72.7mg.


got it! thanks so much!
Answered by ?Unknown?
what are we solving for in this equation?? 15 = n R (T2-T1)
we know n, we know R, we know t1 and t2...so what do we solve for?
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