7. Equilibrium SL

Outline the characteristics of chemical and physical systems in a state of equilibrium

Dynamic Equilibrium- The state at which the rate at which products à reactants is equal to the rate at which reactants à products in a reversible reaction. Concentration, pH, density, and color remain constant.

Reversible Reaction- Reaction in which the newly formed products have the ability to convert back to the reactants (represented by a double face arrowßà)

Concentrations at equilibrium do not necessarily have to be equal, only constant.

Deduce the equilibrium constant expression (K_c) from the equation for a homogenous reaction

How to deduce K_c—the equilibrium constant (ex. 2A + B à 3C + D)

Divide the concentration of the products by the concentration of the reactants and raise those concentrations to a power respective to the coefficient

K­_c = [C]³ [D]

        [A]² [B]

Exceptions: Do not count the following substances in an equilibrium expression

• Solids
• Liquid water IF some of the substances are aqueous

EXAMPLE!!!

Deduce the eq expression for 2SO₂ + 3O₂ à 2SO₃

Kc =    [SO₃]²    .

       [SO₂]²[O₂]³

Deduce the extent of a reaction from the magnitude of the eq constant

When K à 1, the reaction goes almost to completion

When K à 0, the reaction does not proceed as far

Apply Le Chatelier’s Principle to predict the qualitative effects of changes of temperature, pressure, and concentration on the position of equilibrium and on the value of the equilibrium constant.

Le Chatelier’s principle expresses the effect of variables on a reaction’s equilibrium

LE CHATELIER TABLE OF DOOM

Change	Effect on Equilibirum	Effect Kc?
↑ Concentration	Shift to OPPOSITE side	N
↓ Concentration	Shift to SAME side	N
↑ Pressure	Shift to side with LEAST moles of gas	N
↓ Pressure	Shift to side with MOST moles of gas	N
↑ Temperature	Shifts in ENDOTHERMIC direction	Y
↓ Temperature	Shifts in EXOTHERMIC direction	Y
+ Catalyst	No effect	N

Shift just means the concentration of a either the products or reactants increases while the other decreases before stabilizing again

State and explain the effect of a catalyst on an equilibrium reaction

Catalysts will have no effect on equilibrium, as they increase both the rates of forward AND reverse reactions, so there will be no shift

Apply the concepts of kinetics and equilibrium to industrial processes

How does the Haber process involve equilibira?

The equation N_{2 (g)} + H­_{2 (g)} ßà 2NH_{3 (g)} ΔH= -92kJ_. suggests that high pressures would be favored, but it takes a lot of $$$ to maintain those conditions, which means a compromise pressure must be found. It also suggests that low temperatures would be better, but very low temperatures have slow rates, so a compromise temperature is determined to produce the most NH­₃­ per hour. An iron catalyst finely divided (for maximum surface area) is used to speed up the reaction.

How does the Contact Process involve equilibria?

The equation S _(s) + O₂ ßà SO­_{2 (g)} ΔH = -196 kJ suggests a high pressure is favorable, but it takes a lot of $$$ to maintain those conditions, so a pressure of about 2 ATM is used.  It also suggests that low temperatures would be better, but very low temperatures have slow rates, so a compromise temperature is determined to produce the most SO­₂­ per hour. A Vanadium (V) Oxide catalyst (V₂O₅) is used.