[hiiamhere]

Hey everyone, iv got a hw question I cant figure out.

Given: N2_(G) + O2(g)_(G) is in equilibrium with 2NO_(G)
and k_c = 0.200
Find the equilebria concentration of all the species if initially there are 5x10^-4mol of NO in a 10.0L container at 900 degrees C

I tried to set up an I.C.E chart but couldnt understand how the numbers would set up and cant find any equation that would fit this. Any and all help is appreciated

[sdekivit]

I asusme Kc is given for the equilibrium at the condition stated (10 L at T = 900K)

Now the equilibrium will be:

N2 + O2 <--> 2 NO

assume x mol NO reacted --> then 1/2x mol N2 and O2 will be formed.

This turns your equilibrium equation into:

K = (5 x 10^-4 - x)² / 0.25x² = 0.200

[hiiamhere]

After working through the math from your equation, I found x = 5.8x10^-1. Does this sound correct? And if so, would this mean that the answer (equilibrium concentration) of both N₂ and O₂ are both 5.8x10^-1

[sdekivit]

i get 4.1 x 10^-4 for x

[hiiamhere]

Oh, I see how you got that, It was a calculation error on my end. So this problem is basically all math once you get it set up right, no I.C.E chart at all? Would this number be my answer though? Im guessing so since there is 1 mol of both gases at the reactants, so it would make sense that they would be similar, or even the same number.

[sdekivit]

no these are mols and when you assume x mol NO has reacted, then the amount of mol N2 and O2 will be 1/2 x

--> to get concentrations remember your volume is 10L

[hiiamhere]

So if the moles are 4.1x10^-4, and if you half that amount you get 2.05x10^-4, then to get concentration (molar concentration im assuming) it would basically be molarity formula correct?
So M=m/l, or M=(2.05x10^-4)/10? Im getting 2.0x10^-6, but for some reason that doesn't sound right

[sdekivit]

well if you start with 5x10^-4 mol NO in a volume of 10L that's a concentration [NO] = 5 x 10^-5 M the concentrations in equilibrium will be less than this number as no matter will be lost or gained (Lavoisier).

btw 2.05 x 10^-4/10 is not 2.0 x 10^-6.

[hiiamhere]

Ok, I think I got it now. My answer of 2.05x10^-4 sounds familiar to a number he gave us as a 'hint' in lecture.

Thanks for your help sdekivit, I appreciate it