[benjovi]

Hey guys, I've got a problem that I've spent the past two hours trying to solve. I need to convert 0.005 L of Y/s to mL of Z produced (at SATP)/s.

Information given;
Balanced equation: 2 X(s) --> 3 Y(g) + 4 Z(g)
M of X=107g/mol, M of Y=34g/mol, M of Z=28g/mol

The part I don't understand about the question is converting the mL of Y to the mL of Z. I've tried just multiplying by the mole ratio (4/3), but nothing cancels out. Would it be possible to use PV=nRT to find moles of Y, use a mole ratio to find moles of Z, then use PV=nRT again to find L of Z and finally convert that to mL?

[Borek]

Multiplying by mole ratio is a perfectly correct approach. Actually, if you go the other route, everything will cancel out leaving you with exactly the same conversion factor, just after a looooong detour.

IOW: if something doesn't cancel out it doesn't mean there is something wrong with the general approach, it means there is something wrong with the details of your calculations.

[Big-Daddy]

I think there would be a further correction of P(Y)/P(Z) where P(Species) is the pressure of the species. I take it that "STP" in the OP refers to the total mixture.

(BTW I have no idea what to do if V and P are both changing with time for a given species, so P(X) and P(Y) are assumed constant).

Then d/dt(n(Species)) = d/dt(P(Species)*V(Species)/(RT)) and if only V(Species) depends on time then d/dt(n(Species))= P(Species)/(RT) * d/dt(V(Species)). So:

d/dt(n(Y)) = P(Y)/(RT) * d/dt(V(Y))
d/dt(V(Z)) = d/dt(n(Z)) * RT/P(Z)
d/dt(n(Z)) = 4/3 * d/dt(n(Y))

And we find that d/dt(V(Z)) = 4/3 * P(Y)/P(Z) * d/dt(V(Y)). So if (1) the gases can be treated as ideal, (2) the pressure of both individual gases is constant and (3) the pressure of both individual gases is the same then the mole ratio calculation becomes equivalent to the volume ratio calculation (because P/RT is the same on both sides and this just cancels).

[mkurek]

I'm assuming these are ideal gasses we're dealing with here. So then 1 mole of an ideal gas occupies 22.4 Liters

So then take your .005/22.4 to give moles of Y

Then take moles of Y and use stoichiometric conversion factors to convert it to moles of Z.

So then (.005/22.4)(4/3) gives you moles of Z

And then from that moles of Z you can use the fact that a mole is 22.4 L again to determine the volume of Z

[Borek]

Geez, have you all never heard about Avogadro's law? Why do you overcomplicate things? You do long series of calculations only to cancel out everything in the end and prove what is obvious from the very beginning - ratio of volumes equals ratio of stoichiometric coefficients.