Keq Question (TBR)

[jsmith1]

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So it says, "At STP the partial pressure of NO is 152 torr and the partial pressure of O2 is 228 torr and the remainder is NO3. If this mixture is at equil. what is the Keq at STP for the rxn:

NO(g) + O2(g) --> NO3(g)

So I know total pressure is 760 torr at STP. Should it just be (380) / (152 * 228) = 0.01096491228 torr? They want the answer in atm so this should be 1.44 × 10-5 atm? The actual answer is 8.333 atm? HELPP

 

[Brunerm]

You need to convert to atm at the start.
1atm=760torr, so divide each pressure by 760 to convert to atm.
partial pressure of NO=152/760=.2 atm
partial pressure of O2=228/760=.3 atm
At STP, the total pressure equals 1 atm, so 1-(.2+.3)=.5
So at equilibrium the partial pressure of NO3 is .5 atm.
Now set up the equilibrium equation: Keq=[NO3]/([O2][NO])=.5/(.2*.3)=8.33

edit: the reason your way didn't get you the right answer is because Keq is unitless, so you cannot find Keq in torr and then convert to atm.