An ICE Table can be used to find the concentrations of all aqueous and gaseous reactants and products when a chemical reaction achieves equilibrium. It is a method of organizing stoichiometric calculations, and its letters stand for the following:
All three are measured in mol/L, and they are related by I `+` C `=` E.
In the reaction H_{2(g)} + I_{2(g)} ⇌ 2 HI_{(g)}, 2.00 mol of H_{2(g)} and 3.00 mol of I_{2(g)} are placed in a 1.00 L container. Calculate the other two equilibrium concentrations if I_{2(g)} has an equilibrium concentration of 1.30 mol/L.
Here is the I calculation for H_{2(g)} (you don’t need to show all of them):
`c = n/V = (2.00\ "mol")/(1.00\ "L") = 2.00\ "mol/L"`.
Let `x` represent the absolute value of the change in concentration of H_{2(g)}. This can also be written more concisely like this: let `x = |Delta ["H"_2]|`.
When writing the let statement for `x`, always choose a reactant or product that has a coefficient of 1. This way, you can simply fill in all the C values with `-ax` for reactants and `+ax` for products, where `a` is the coefficient for that reactant or product.
H_{2(g)} | I_{2(g)} | 2 HI_{(g)} | |
I | `2.00` | `3.00` | `0` |
C | `-x` | `-x` | `+2x` |
E | `2.00 − x` | `3.00 − x` | `2x` |
The E value for I_{2(g)} is known to be 1.30 mol/L, but our table tells us that it is also `x` subtracted from 3.00 mol/L, therefore we can set them equal:
`1.30\ "mol/L" = 3.00\ "mol/L" - x`,
`x = 1.70\ "mol/L"`.
By substituting 1.70 mol/L for `x` into the E expressions for H_{2(g)} and HI_{(g)}, we can easily find their concentrations at equilibrium as well (0.30 mol/L and 3.40 mol/L respectively).