Concentration at equilibrium
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:
- [I]nitial concentration
- [C]hange in concentration
- [E]quilibrium concentration
All three are measured in mol/L, and they are related by I C E.
In the reaction H2(g) + I2(g) ⇌ 2 HI(g), 2.00 mol of H2(g) and 3.00 mol of I2(g) are placed in a 1.00 L container. Calculate the other two equilibrium concentrations if I2(g) has an equilibrium concentration of 1.30 mol/L.
Here is the I calculation for H2(g) (you don’t need to show all of them):
Let represent the absolute value of the change in concentration of H2(g). This can also be written more concisely like this: let .
The E value for I2(g) is known to be 1.30 mol/L, but our table tells us that it is also subtracted from 3.00 mol/L, therefore we can set them equal:
By substituting 1.70 mol/L for into the E expressions for H2(g) and HI(g), we can easily find their concentrations at equilibrium as well (0.30 mol/L and 3.40 mol/L respectively).