ice tables.notebook
April 22, 2016
Warm Up: The reaction involving the formation of hydrogen bromide takes place in a 2.0 L vessel at 50oC. At equilibrium, the mixture was analyzed and was found to contain 0.090 moles of HBr and 1.7x10­4 moles of hydrogen. If the Keq for this system at 50oC is 4.2 x 10­9 , calculate the concentration of bromine at the point of equilibrium.
Nov 17­3:13 PM
Keq calculations: Calculating Keq and equilibrium concentrations given initial concentrations and one equilibrium concentration
The problems we have looked at so far involve calculations where the concentrations of reactants are products are known at the point of equilibrium. Often, we do not have all this information. Given the starting amounts of reactants and the amount of at least one substance at equilibrium, we can find all equilibrium concentrations and Keq.
Example: Synthesis gas (a mixture of CO and H2) is increased in concentration of hydrogen by passing it with steam over a catalyst. Some of the CO is converted to CO2, which can be removed.
CO(g) + H2O(g) ↔ CO2(g) + H2 (g)
Suppose you start with a gaseous mixture containing 1.00 mol/L CO and 1.00 mol/L H2O. When equilibrium is reached at 1000°C, the mixture contains 0.43 mol/L H2. What are the equilibrium concentrations of each substance and the value of Keq?
Solution: Set up an ICE table (initial/change/equilibrium)
Let x = [CO] that reacts
Concentration (mol/L)
CO(g) + H2O(g) ↔ CO2(g) + H2 (g)
Initial
Change
Equilibrium
Nov 17­3:18 PM
1
ice tables.notebook
April 22, 2016
Example 2: Hydrogen sulfide, a colorless gas with a foul odor, dissociates on heating:
2H2S(g) ↔ 2H2(g) + S2 (g)
When 0.100 mol H2S was put into a 10.0 L vessel and heated to 1132°C, it have an equilibrium mixture containing 0.0285 mol H2. What is the value of Keq at this temperature?
Solution: First, calculate concentrations with moles given:
Now set up an ICE table. Initial
Change
Equilibrium
Nov 17­3:23 PM
Practice Problems: 1. A mixture of iron(III) nitrate and potassium thiocyanate, in aqueous solution, react to form the iron(III) thiocyanate ion, Fe(SCN)2+, according to the equation:
Fe3+(aq) + SCN­(aq) ↔ Fe(SCN)2+(aq)
If the initial concentration of Fe3+ is 0.0064M, the initial concentration of SCN­ is 0.0010M, and the concentration of Fe(SCN)2+ at equilibrium is 4.5 x 10­4M, calculate Keq.
2. 1.00 mol of CO2 and 1.00 mol of H2 are placed in a 1.00 L flask at 825K and react according to:
CO2(g) + H2(g) ↔ CO(g) + H2O(g)
Analysis of the equilibrium mixture shows 0.27 mol of CO present. Determine Keq at this temperature.
Complete the following problems from the text: Page 508 #13, Page 516 #2, Page 536 #12
Nov 17­3:23 PM
2
ice tables.notebook
April 22, 2016
Nov 26­3:21 PM
Nov 26­3:20 PM
3