[JessMaksut]

If 2.5 mol of H2 (g), 1.5 mol I2 (g), and 7.5 mol HI (g) are placed in the same container (1.00 L) at 430 degrees C which way would the equilibrium shift? Show all work.

In class, I was told that if Q > K, there is too much of the reactants, so to get it to equilibrium, the reaction shifts forward. I Q > K, there is too much product, so to get it to equilibrium, the reaction shifts backward or reverse. If Q = K, the reaction is at equilibrium.

I also know that you need to convert mols to M, so to do that, you must divide by number of liters of solution.

Therefore, 2.5 mol H2/1.00 L is just = 2.5 M. The same is done with the other two, resulting in 1.5 M for I2 and 7.5 M for HI.

Wouldn't Q = [HI]2 / [H2][I2] or [7.5 M]2 / [1.5 M][2.5 M]?

Therefore the answer would be 15. But how am I supposed to get the K value? I'm completely confused.

[Borek]

If you are not given K you can't solve the question in general. But you were given K in other question, weren't you?

You may try to guess what is more stable - mixture of I₂ and H₂ (both highly reactive) at elevated temperature, or product of their reaction (HI).