[H Mac]

Consider the following reation, which takes place in an autoclave at 250'C and 800 atm.
       NH3(g)  + 7/4 O2(g) -->  NO2 (g) +  3/2 H2O(g)
Into the reaction vessel has been placed 200L of NH3(g) and 120L of O2(g). The reaction is allowed to go to completion.
Determine the quantity, in moles, of the gas that remains unreacted.


Just some hints as to what I might do here would be fantastic!

[Arkcon]

PV=nRT

200L of NH3 at 250 C and 800 atm is how many moles?

The units of a chemical reaction are moles

[sjb]

PV=nRT

200L of NH3 at 250 C and 800 atm is how many moles?

Could be wrong, but do you really need to know this? If the reaction "goes to completion", one or other of the reactants is in excess, and, that's the figure you need for the answer?

[Borek]

PV=nRT

200L of NH3 at 250 C and 800 atm is how many moles?

Could be wrong, but do you really need to know this? If the reaction "goes to completion", one or other of the reactants is in excess, and, that's the figure you need for the answer?

Interesting point. One problem - the volume is changing during reaction, so it is not obvious what the final pressure is. Converting to moles first you ignore these changes.

[Arkcon]

PV=nRT

200L of NH3 at 250 C and 800 atm is how many moles?

Could be wrong, but do you really need to know this? If the reaction "goes to completion", one or other of the reactants is in excess, and, that's the figure you need for the answer?

Interesting.  Using an integer balanced equation (note to original poster, this is not needed, it's just easier:)

4 NH3(g)  + 7 O2(g) --> 4 NO2 (g) +  6 H2O(g)

Nope, see like Borek says, n is different before and after.  This is typical beginning chemistry problem, convert from one set of units, plug into equation, then convert back.