1. AT YOUR SEAT DEMO --- THE START OF CHAPTER 13
1 TEST TUBE RACK
3 TEST TUBES
FILL ONE TEST TUBE HALF WAY WITH KSCN SOLUTION
FILL PIPETTE ONE EIGHTH OF THE WAY WITH Fe(NO3)3 SOLUTION AND PLACE PIPETTE IN THE SECOND TEST TUBE
PLACE A FEW CRYSTALS OF WHITE SOLID ON WEIGHING PAPER WITH FORCEPS

2. KSCN(aq) + Fe(NO3)3(aq) →←
SCN-(aq) + Fe3+(aq) → FeSCN2+(aq)
Of Note: Chemical Reactions are Reversible!
Chemical Equilibrium: When the rates of the forward and the reverse reactions in a closed chemical system are equal.

3. It was discovered, in the 1860’s, that if we treat these concentrations at equilibrium in a special way we see something significant
[R]
concentration →
[P]
 Equilibrium established
time→
forward
Reaction Rate →
reverse
time→

4. aA + bB ↔ cC + dD [C]c [D]d = Keq [A]a [B]b [FeSCN2+] [SCN-] [Fe3+]
Active mass was defined in the as "the amount of substance in the sphere of action"
aA + bB ↔ cC + dD
[C]c [D]d
Mass action expression
= Keq
[A]a [B]b
Equilibrium Constant
…for the iron thiocyanate complex forming…
Guldberg and Waage …uncovered the relationship.
[FeSCN2+]
[SCN-] [Fe3+]

5. The formation of ammonia gas
and
The precipitation of iron (III) hydroxide from iron (III) nitrate and sodium hydroxide solutions

6. ½ N2(g) + 3/2 H2(g) ↔ NH3(g)
Keq = [NH3]
[N2]1/2 [H2]3/2

7. Fe(NO3)3(aq) + 3NaOH (aq) ↔ 3NaNO3(aq) + Fe(OH)3(s)
Keq = [NaNO3]3
[Fe(NO3)3] [NaOH]3
(Don’t include solids and liquids in mass action expressions…they don’t have an active mass!)