Keq question..pleaseeeee help me

[Tina324]

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From achiever test #2:

What is the Keq at 400 K if 3 moles of CO2 introduced into 2 Liter container are 20 percent dissociated at quilibrium?
2CO2<--> 2 CO + O2

This is what the answer key says:
3moles/2L=1.5M

1.5M x 20%=.3M
1.5M-.3M=1.2M

Keq=[CO]^2 [O2] / [CO2]^2
according to the red equation the reaction produces 1 mole O2 for every 2 moles of CO so CO=.15M

Therefore Keq=(.3)^2 (.15) /(1.2)^2

I think i understand the above, BUT i don't get it CONCEPTUALLY...like, if we are starting out with 3 moles of CO2 and 20 percent of that dissociates...shouldn't the TOTAL concentration of the products equal .3M? shouldn't the concentration of CO=.2M and O2=.1M since CO:O2 is a 2:1 ratio?

Please pleas please help me out with this guys...if you don't understand what i am asking, let me know.

thank you so much. DAT in a weeeeeek😳

 

[Tina324]

bumpity bump bump😳

 

[peerless218]

wow..that kinda problem probably wont be on the test. My gen chem was kinda easy. mostly conceptual problems and easy equation setting problems. I doubt problems of such difficulty would appear

 

[Tina324]

haha im worried abt the conceptual too! what exactly denotes a conceptual? can u give me examples of the types of q's (obviously not the actual q's lol)
the only things i can think abt are b.p., mp, acid strength, hmm wat else?

 

[Tina324]

any ideas on this problem? i saw one in schiever and top score!!