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

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.

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→

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+]

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

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

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!)