Using the RICE method to calculate and
manipulate equilibrium expressions.
RICE
R is the balanced equation for the reaction
I is initial concentration
C is change in the concentration
E is the equilibrium concentrations
Solving calculations
1. Set up the RICE table
2. Set up the equilibrium expression and set it equal
to its value, if given
3. If given equilibrium concentrations skip down to
E and put them in
4. If given K use it to solve for x and use x to
calculate the equilibrium concentrations.
Hints
• If K is 10-5 x is negligible
• If K is large look to square both sides
• If none of the above apply you will need to use
the quadratic formula.
For the gas phase reaction
H2(g) + I2(g) = 2 HI(g)
Kc = 50.3 at 731 K. Equal amounts (0.100 M each) are introduced
into a container, and then the temperature is raised to 731 K.
Calculate the concentration of each when the system is at
equilibrium.
At 1100 K, Kc = 4.20 x 10-6 for the gas phase reaction,
2 H2S(g) ! 2 H2(g) + S2(g)
What concentration of S2 can be expected when 0.200 mole of H2S comes to
equilibrium at 1100 K in an otherwise empty 1.00-L vessel?
Problems
•
1.00-L container contains 1.00 M of phosgene, which decomposes according
to the reaction,
COCl2(g) ! CO(g) + Cl2(g).
At equilibrium, the concentration of Cl2 is 0.028 M. What is the
concentration of CO?
•
A 1.00-L container contains 1.00 M of phosgene, which decomposes
according to the reaction,
COCl2(g) ! CO(g) + Cl2(g).
At equilibrium, the concentration of Cl2 is 0.028 M. What is the equilibrium
constant?
•
A 2.00-L container contains 1.00 mole each of H2 and I2 gases. When the
system reached equilibrium, the concentration of I2 is 0.11. The equilibrium
equation is
H2(g) + I2(g) ! 2 HI(g)
What is the concentration of HI?
•
A 2.00-L container contains 1.00 mole each of H2 and I2 gases. When the
system reached equilibrium, the concentration of I2 is 0.11. The equilibrium
equation is
H2(g) + I2(g)
! 2 HI(g)
What is the equilibrium constant?
•
A 1.00-L container contains 1.00 mole each of H2 and I2 gases. The
equilibrium constant Kc = 50 for the equilibrium
H2(g) + I2(g) ! 2 HI(g).
What is the concentration of H2?
Chloromethane, CH3Cl, which has been used as a refrigerant and a local
anesthetic, can be made from the following reaction.
CH3OH(g) + HCl(g)
CH3Cl(g) + H2O(g)
KP = 5.9 × 103 at 120 °C
If enough methanol and hydrogen chloride are added to a container at 120 °C to
yield an initial pressure of 0.75 atm for each, what will the equilibrium pressures
of all of the reactants and products be?
Exercise 8 Calculating Equilibrium Pressures I
Dinitrogen tetroxide in its liquid state was used as one of the fuels on the lunar lander for
the NASA Apollo missions.
In the gas phase it decomposes to gaseous nitrogen dioxide:
N2O4(g) <=> 2 NO2(g)
Consider an experiment in which gaseous N2O4 was placed in a flask and allowed to
reach equilibrium at a temperature
where Kp = 0.133. At equilibrium, the pressure of N2O4 was found to be 2.71 atm.
Calculate the equilibrium pressure of
NO2(g).
Exercise 9 Calculating Equilibrium Pressures II
At a certain temperature a 1.00-L flask initially contained 0.298 mol PCl3(g) and 8.70 ×
10-3 mol PCl5(g). After the system had reached equilibrium, 2.00 × 10-3 mol Cl2(g) was
found in the flask. Gaseous PCl5 decomposes according to the reaction
PCl5(g) <=> PCl3(g) + Cl2(g)
Calculate the equilibrium concentrations of all species and the value of K.
Exercise 10
Carbon monoxide reacts with steam to produce carbon dioxide and hydrogen. At 700 K
the equilibrium constant is 5.10. Calculate the equilibrium concentrations of all species if
1.000 mol of each component is mixed in a 1.000-L flask.
Assume that the reaction for the formation of gaseous hydrogen fluoride from hydrogen
and fluorine has an equilibrium constant of 1.15 × 10 at a certain temperature. In a particular
2
experiment, 3.000 mol of each component was added to a 1.500-L flask. Calculate the equilibrium
concentrations of all species.
Assume that gaseous hydrogen iodide is synthesized from hydrogen gas and iodine vapor
at a temperature where the equilibrium constant is 1.00 × 102. Suppose HI at 5.000 × 10-1
atm, H2 at 1.000×10-2 atm, and I2 at 5.000 × 10-3 atm are mixed in a 5.000-L flask.
Calculate the equilibrium pressures of all species.