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physgirl

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## Homework Statement

A chemist studying the rxns of pollutant SO2 places a mixture of SO2 and O2 in a 2.0L container at 900K and an P[init]=1.95 atm. When rxn occurs, gaseous SO3 forms and P falls to 1.65 atm. How many moles of SO3 formed?

## Homework Equations

PV=nRT but I'm not sure what else...

## The Attempt at a Solution

I was assuming both SO2 and O2 in the starting material are gases? So I used V=2L, P=1.95atm, and T=900K to find the number of moles of both gases combined, which turned out to be ~0.053 moles. And I'm not sure what to do with this number to get to the answer... I wrote out the balanced equation to be: 2SO2(g) + O2(g) --> 2SO3 (g) although I don't know if that matters... I can't assume that T stays the same, can I? the problem doesn't say anything about it...

[edit] wait, can I start out by saying that... since you're not losing any gas, #moles of starting material (SO2+O2) has to be the same as #moles of final mixture (SO3+(leftover)SO2+O2)... and so use 0.053moles, given final pressure (1.65atm) and 2L (since it's a container it doesn't expand..?) to find the final temperature and go from there somehow?

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