[the rael walter white]

For the reaction 2HI -> H2 + I2 (all gas phase) the value of the equilibrium constant at 700K is 0.0183. If 3.0 moles of HI are placed in a 5-liter vessel and allowed to decompose according to the above equation, what percentage of the original HI would remain at equilibrium

Can someone explain why the equilibrium concentration constant for 2HI IS .6-X AND NOT .6-2X when filling out the ice table

[Borek]

Can you show complete ICE table for this problem? A lot depends on what x refers to.

[Orcio_87]

Initial concentration of HI is 0,6 mol / liter, so final concentrations of HI, H₂ and I₂ are 0,6 - x, 1/2 x and 1/2 x (two molecules of HI produces only one H₂ and one I₂).

[Borek]

Initial concentration of HI is 0,6 mol / liter, so final concentrations of HI, H₂ and I₂ are 0,6 - x, 1/2 x and 1/2 x (two molecules of HI produces only one H₂ and one I₂).

Or 0.6-2x, x and x, depending on what the x is. Both approaches are OK, it is just about knowing which one you use and what you solve for.

[the rael walter white]

I totally agree but the solution we were given below confuses the heck out of me

[the rael walter white]

Do you guys think this guy is right or am I just completely lost

[Borek]

Do you guys think this guy is right or am I just completely lost

No, this solution is incorrect and you are perfectly right being confused. Stoichiometric coefficient of 2 is missing (either as just "2" or as "1/2").