Quantitative Changes in Equilibrium systems
Reminders:
-temperature affects K
-we are only looking at closed systems
-Large K = lots of products; K= 1 is equilibrium, small K = lots of reactants
Reaction Quotient (Q)
-used if concentrations are known and want to know if system is at
equilibrium or which direction the reaction will proceed in if not at Eq
-To find Q: substitute current concs. into equilibrium law equation and
solve
-Q is like K but concs aren’t necessarily at equilibrium
If:
1. Q = K
2. Q > K
3. Q < K
system is at Equilibrium
reaction must shift to reverse (left/reactants) to get to Eq
reaction must shift to forward (right/products) to get to Eq
Example #1: Calculating equilibrium concentrations from knowns:
Sulfur trioxide is a compound used in the production of sulfuric acid. It
is produced by reacting sulfur dioxide with oxygen according to the
following equation:
Calculate the equilibrium concentration of oxygen if 1.50mol/L sulfur
dioxide and 3.50mol/L sulfur trioxide are found in an equilibrium mixture
of this system at 600 K. K for the reaction at this temperature is 4.30.
Example #2: Calculating equilibrium concentrations from initial
concentrations (ice table!!)
When hydrogen reacts with fluorine, hydrogen fluoride is formed
according to the following equation:
The equilibrium constant K is 1.5 x 102 at SATP. Calculate the
concentrations of all entities at equilibrium if 4.00mol of hydrogen,
4.00mol of fluorine and 6.00mol of HF are initially placed into a 2.00L
reaction vessel.
Example #3:
Calculating equilibrium concentrations when K is very small (imperfect
squares)
Nitrosyl chloride, NOCl decomposes to form nitrogen monoxide and
chlorine gas according to the following equation:
At 35 Celsius, Keq is 1.60 x 10-5 . Calculate the concentration of all entities
at equilibrium if 0.80mol NOCl is placed in an evacuated 2.00L container
at this temperature and allowed to reach equilibrium.
Example #4: Calculating equilibrium concentrations involving a Quadratic
equation.
When hydrogen and iodine are placed in a closed container at 440 Celsius,
they react to form hydrogen iodide. At this temperature, the equilibrium
constant, K is 49.7. Determine the concentrations of all entities at
equilibrium if 4.00mol of hydrogen and 2.00 mol of iodine are placed in a
2.00 L reaction vessel.