CHEMICAL EQUILIBRIUM

Finding a balance (between reactants & products)

CHEMICAL EQUILIBRIUM

Has been reached when the concentration of reactants and products are constant

Dynamic equilibrium : The rate of formation of reactants = the rate of formation of products.

K2S(aq) + CaF2(aq) 2KF(aq) + CaS(s)

CaS(s) Ca+2(aq) + S-2

(aq)

THE EQUILIBRIUM CONSTANT – KEQ (OR JUST K)

K = [products]coefficients / [reactants]coefficients

For aX + bY cZ, Keq = [Z]c / [X]a[Y]b

What does it (K) mean? If K < 1…

Reactants are favored. If K > 1…

Products are favored. If K = 1…

Both (or neither) are favored.

THE AFFECTS OF PRESSURE

only pertain to gases

Kp = gaseous equilibrium constant

 

K = Kp(RT)

HETEROGENEOUS SYSTEMS

Contain more than one phase (solid, liquid or gas)

By definition…(moles/liter)

[“pure” solid] or [“pure” liquid] = 1

For CaS(s) Ca+2(aq) + S-2

(aq)

k = [Ca+2 ]x[S-2] / 1

APPLICATIONS

The value of K determines… reaction likelyhood NOT reaction rate.

(See Ch 12.)

The reaction quotient Q = [products]coefficients /

[reactants]coefficients

for the initial conditions…Compare Q & K to determine which way

the reaction is likely to proceed.

SOLVING EQUILIBRIUM PROBLEMS (RICE) Reaction Equation : Find K. Find

[ ]’s. Calculate Q (from Initial concentrations).

Compare K & Q (final vs. initial concentrations).

Solve (unknowns to achieve Equilibrium).

LE CHATELIER’S PRINCIPLE

A system at equilibrium will respond to a disruption by moving back toward equilibrium.

wrt P..Increasing P favors smaller volumes. (gases)

wrt [ ]…Increasing [ ] of reactants favors products and vice versa.

wrt T…Increasing T favors endothermic reactions and works against exothermic reactions.