Name: _________________________________________ Date: ________________ Mods: ____________
Equilibrium Calculations Using the “ICE” Tables
Type 1: Calculating K from Initial and Equilibrium Concentrations
1) These kinds of problems will give at least one equilibrium concentration however the value of the equilibrium
constant, K, will NOT be given.
2) Make sure you have a balanced chemical reaction.
3) Transfer any initial concentrations (or partial pressures) of reactants given in the problem into the “I” row of the ice
table. [Note that the initial concentrations of all products in a reaction will always be zero!!!]
4) If any equilibrium concentrations are given, transfer these values into the “E” row of the ice table.
5) Calculate the change in concentrations of any reactants and/or products for which BOTH the initial concentration
and equilibrium concentration are known. For reactants/products in which ONLY the initial concentration is known,
the change in concentration can be determined using stoichiometry if you begin with one of the change in
concentrations which IS known (use the balanced coefficients to convert from one substance to another).
[Note that the change in REACTANTS must always be subtracted because we are using up the reactants
to form products. Similarly, the change in PRODUCTS must always be added because we are forming more
products.]
6) The goal is to determine all the equilibrium concentrations in the ice table. With this known, the equilibrium
expression can be written and all the equilibrium concentrations may be plugged into the expression to solve for
the equilibrium constant, Keq (aka: Kc or Kp)
7) Note that NO pure solids or pure liquids will appear in ICE tables because they do not appear equilibrium
expressions.
Example #1: A closed system initially containing 1.000 x 10-3 M H2 and 2.000 x 10-3 M I2 at 448°C is allowed to reach
equilibrium. Analysis of the equilibrium mixture shows that the concentration of HI is 1.87 x 10 -3 M. Calculate Keq at
448°C for this reaction:
____ H2 (g) + ____ I2 (g)  ____ HI (g)
Initial
Change
Equilibrium
Example #2: Sulfur trioxide decomposes at a high temperature in a sealed container. Initially, the vessel is charged at
1000 K with SO3 (g) at a partial pressure of 0.500 atm. At equilibrium, the SO 3 partial pressure is 0.200 atm. Calculate
the value of Keq at 1000 K for this reaction:
____ SO3 (g)  ____ SO2 (g) + ____ O2 (g)
I
C
E
3. Inside a sealed vessel, 0.025 atm SO2 and 0.020 atm O2 at 1000 K react to form 0.0162 atm SO3 at equilibrium.
What is the Keq for this reaction?
____ SO2 (g) + ____ O2 (g)  ____ SO3 (g)
I
C
E
4. An aqueous solution of 0.00325 M Fe3+ was reacted with 0.0020 M SCN– at 25oC. Calculate the value of Keq for
this reaction when the equilibrium concentration of FeSCN 2+ is 0.000667 M.
Fe3+ (aq) + SCN- (aq)  FeSCN2+ (aq)
I
C
E
5. At a certain temperature, 1.0 M NH3 is introduced into a sealed container. At equilibrium, the concentration of
NH3 is only 0.50 M. Find the value of Keq for this reaction:
____ NH3 (g)  ____ N2 (g) + ____ H2 (g)
I
C
E
Equilibrium Calculations Using the “ICE” Tables
Type 2: Calculating Equilibrium Concentrations from Initial Concentrations
Notes:
1) These kinds of problems will give the value of the equilibrium constant, K in the problem, but the equilibrium
concentrations are NOT given.
2) Make sure you have a balanced chemical reaction.
3) Transfer any initial concentrations (or partial pressures) of reactants given in the problem into the “I” row of the ice
table. [Note that the initial concentrations of all products in a reaction will always be zero!!!]
4) Since NO equilibrium concentrations are known, the change in concentrations are also unknown. Therefore, in
the “C” row of the ice table, changes in concentration will be given in terms of the variable “x”. The value of “x” is
still based on stoichiometry so the multiple of “x” (x, 2x, 3x, etc) is based on the balanced coefficient in front of
each reactant and product. [Note that the change in REACTANTS must always be subtracted because we
are using up the reactants to form products. Similarly, the change in PRODUCTS must always be added
because we are forming more products.]
5) For the “E” row in the ice table, the equilibrium concentration is equal to the initial concentration plus or minus
(depending if it is a product or reactant, respectively) the “x” change in concentration.
6) Write the equilibrium expression for the reaction and set in equal to the known Keq value given in the problem.
With the equilibrium concentrations known in terms of “x”, plug these values into the equilibrium expression and
solve it for the value of “x”. [Note that when you have x2 in the equilibrium expression, you must solve for x
using the quadratic formula]
7)
Once the value of “x” is known, solve for all equilibrium concentrations. [Note that if there are two possible values
for “x”, solve the equilibrium concentrations for each “x” value. If one value of “x” results in negative equilibrium
concentrations, this is NOT a meaningful value of “x” and should be ignored.
Example 1: A sealed flask is filled with 1.0 M H2 and 2.0 M I2 at 448°C. The value of the equilibrium constant Keq for the
reaction at this temperature is 50.5. What are the equilibrium concentrations of H 2, I2 and HI?
____ H2 (g) + ____ I2 (g)  ____ HI (g)
I
C
E
Example 2: For the reaction below, the equilibrium constant Keq has the value 0.497 at 500 K. A gas cylinder at 500 K is
charged with PCl5 at an initial pressure of 1.66 atm. What are the equilibrium pressures of PCl 5, PCl3, and Cl2 at this
temperature?
____ PCl5 (g)  ____ PCl3 (g) + ____ Cl2 (g)
I
C
E
3. At 2000°C, the equilibrium constant for the reaction below is Kc = 2.4 x 103. If the initial concentration of NO is
0.200 M, what are the equilibrium concentrations of NO, N2, and O2?
2 NO (g)  N2 (g) + O2 (g)
I
C
E
4. For the reaction below, the equilibrium constant K c = 7.0 at 400 K. If 0.30 M Br2 and 0.30 M Cl2 are introduced
into a sealed container at 400 K, what will be the equilibrium concentrations of Br 2, Cl2, and BrCl?
Br2 (g) + Cl2 (g)  2 BrCl (g)
I
C
E