Untitled - Kelly Walsh High School

216 CHEMISTRY FOR THE UTTERLY CONFUSED
This is in the quadratic form, and, as such, requires you to use the quadratic
equation.
x
b 2b 2 4ac
2a
In this case, a 4, b 3.76 10 5 , and c 1.88 10 5 . If we enter these values
into the quadratic equation we get x 2.16 10 3 or x 2.17 10 3 .
The quadratic equation always gives two answers. We can eliminate one of the
answers since it is physically impossible to have a negative concentration. This
leaves us with only the positive root. If we enter this answer into the bottom line
of our table, we get the following equilibrium concentrations:
[I 2] 0.500 2.16 10 3 0.498 M
[I] 2(2.16 10 3 ) 4.32 10 3 M
A chemical equilibrium results when two exactly opposite reactions occur at the
same place, at the same time, and with the same rate. An equilibrium constant
expression represents the equilibrium system. Le Châtelier’s principle describes
the shifting of the equilibrium system due to changes in concentration, pressure,
and temperature.
1. The values in a reaction quotient, Q, or an equilibrium constant expression,
K, may be in terms of what two factors?
2. The terms in the numerator of an equilibrium constant expression are always
the ____.
3. The reactants appear on which side of the reaction arrow in an equilibrium
equation?
4. True/False. An equilibrium must respond to the stress created by a catalyst.
5. True/False. Increasing the pressure applied on the system is important for
the equilibrium H 2(g) Br 2(g) K 2 HBr(g).
6. True/False. Adding calcium oxide, CaO, to the following equilibrium will
have no effect. CaCO 3(s) K CaO(s) CO 2(g)
7. True/False. Equilibrium constant expressions never include solids.
8. True/False. Water is important in equilibrium expressions for aqueous
solutions.
9. Write K c expression for each of the following equilibria.
a. CH 4(g) 2 O 2(g) K CO 2(g) 2 H 2O(g)
b. Fe 2O 3(s) 3 CO(g) K 2 Fe(s) 3 CO 2 (g)
c. HNO 2(aq) K H + (aq) NO 2 (aq)
d. Cu 2 (aq) 4 NH 3(aq) K Cu(NH 3) 4 2+ (aq)
e. ZnCO 3(s) K Zn 2 (aq) CO 3 2 (aq)