A RICE chart or RICE box or ICE table is a tabular system of keeping track of changing concentrations in an equilibrium reaction. RICE stands for reaction, initial, change, equilibrium. It is used in chemistry to keep track of the changes in amount of substance of the reactants and also organize a set of conditions that one wants to solve with.
Example
To illustrate the processes, consider the case of dissolving a weak acid, HA, in water. The pH can be calculated using a RICE chart. Note that in this example, we are assuming that the acid is not very weak, and that the concentration is not very dilute, so that the concentration of ions can be neglected. This is equivalent to the assumption that the final pH will be below about 6 or so. See Calculations of pH for more details. First write down the equilibrium expression. This is generally regarded as the 'R'. The columns of the table correspond to the three species in equilibrium.
R
I
Ca
0
0
C
-x
+x
+x
E
Ca - x
x
x
The first row, labeled I, has the initial conditions: the nominal concentration of acid is Ca and it is initially undissociated, so the concentrations of A− and H+ are zero. The second row, labeled C, specifies the change that occurs during the reaction. When the acid dissociates, its concentration changes by an amount, and the concentrations of A− and H+ both change by an amount. This follows from consideration of mass balance and charge balance. Note that the coefficients in front of the "x" correlate to the mole ratios of the reactants to the product. For example, if the reaction equation had 2 H+ ions in the product, then the "change" for that cell would be "2x" The third row, labeled E, is the sum of the first two rows and shows the final concentrations of each species at equilibrium. It can be seen from the table that, at equilibrium, = x. To findx, the acid dissociation constant must be specified. Substitute the concentrations with the values found in the last row of the ICE table. With specific values for Ca and Ka this quadratic equation can be solved for x. Assuming that pH = -log10 the pH can be calculated as pH = -log10x. If the degree of dissociation is quite small, Ca ≫ x and the expression simplifies to and pH = 1/2. This approximate expression is good for pKa values larger than about 2 and concentrations high enough.
