Equilibrium state of balance condition in which opposing forces exactly balance/equal each other need 2-way or reversible situation need a closed system

Dynamic Equilibrium macroscopic level –looks like nothing is happening microscopic level –lots going on

3 Kinds of Equilibria phase equilibrium – physical solution equilibrium – physical chemical equilibrium - chemical

Phase Equilibrium phase changes are reversible processes H 2 O(l)  H 2 O(g) H 2 O(l)  H 2 O(s) same substance on both sides only its phase is different

Examples - Phase Equilibrium water & water vapor in sealed bottle perfume in partially full, sealed flask ice cubes & water in insulated container dry ice & CO 2 (g) in a closed aquarium

Solution Equilibrium: Solids saturated solution = dynamic equilibrium dissolving & solidification occur at equal rates

Solid in Liquid NaCl(s)  NaCl(aq) Favored a little bit by higher temperature

Solution Equilibrium: Gases CO 2 in water CO 2 (g)  CO 2 (aq) favored by high pressure & low temperature

Reversible Reactions N 2 (g) + 3H 2 (g)  2NH 3 (g) forwardforward: –N 2 & H 2 consumed; NH 3 produced 2NH 3 (g)  N 2 (g) + 3H 2 (g) reversereverse: –NH 3 consumed; N 2 & H 2 produced

Reversible Reactions: 1 Equation N 2 (g) + 3H 2 (g)  2NH 3 (g) forward reaction: reactants on L –read left to right reverse reaction: reactants on R –read in reverse: right to left reaction runs in both directions all the time

Time Concentration NH 3 H2H2 N2N2 N 2 (g) + 3H 2 (g)  2NH 3 (g) Why is this point significant?

Reaction Rate depends on concentration of reactants as concentration reactants ↓, rate forward reaction ↓ as concentration product ↑, rate reverse reaction ↑

Chemical Equilibrium state in which forward & reverse rxns balance each other Rate forward rxn = Rate reverse rxnRate forward rxn = Rate reverse rxn does this mean concentrations reactants/products are equal? NO!

Chemical Equilibrium Rate forward rxn = Rate reverse rxn constantat equilibrium: concentrations all species are constant –stop changing –rarely ever equal

Reversible Reactions vs. Reactions that “Go to Completion” If goal is to maximize product yield: easier in reaction that goes to completion –use up all reactants –left with only product Reversible reactions are different look at  conc/  time picture again

Time Concentration NH 3 H2H2 N2N2 N 2 (g) + 3H 2 (g)  2NH 3 (g) Original Equilibrium Point

Reversible Reactions once reach equilibrium, don’t produce any more product –bad news if product is what you’re selling can you change the equilibrium concentrations? if so how can it be done? for example, how can you maximize product?

What you would really like to see…

lots of product created as fast as possible New equilibrium point

equilibrium can be changed or affected by: – any factor that affects forward and reverse reactions differently

What factors affect rate of rxn? concentration/pressure (gases only) temperature presence of catalyst

Catalyst same effect on both forward & reverse reactions equilibrium reached more quickly, but “equilibrium point” not shifted equilibrium concentrations are same with or without catalyst

Concentration, Pressure, Temperature changes in concentration, pressure, temperature affect forward & reverse reactions differently composition of equilibrium mixture will shift to accommodate these changes

LeChatelier’s Principle “If system at equilibrium is subjected to stress, the system will act to reduce stress” stress = change in concentration, pressure, or temperature system tries to undo stress

System only 2 possible actionsonly 2 possible actions shift to rightshift to right & form more product –forward reaction speeds up –forward reaction speeds up more than reverse reaction shift to leftshift to left & form more reactant –reverse reaction speeds up –reverse reaction speeds up more than forward reaction

A + B  C + D ( at equilibrium ) If ↑ concentration A, how will system react? How does new equilibrium mixture compare to original equilibrium mixture? Use logic: –If you ↑ [A]: the system wants to ↓ [A] must use A up, so forward reaction speeds up

A + B  C + D DEC  ______ INC  left  [B] INC  ______ DEC  right  [C] ______ DEC  INC  left  [D] INC  DEC  ______right  [A] [D][C][B][A]Equil. Shift Stress

Changes in Temp exothermic reaction: A + B  C + D + heat consume –If ↑ temperature, system shifts to consume heat so shifts to left endothermic reaction: A + B + heat  C + D –If ↑ temperature, system shifts to consume heat so shifts to right

Changes in Pressure N 2 (g) + 3H 2 (g)  2NH 3 (g) If ↑ pressure, system shifts to side with fewer moles of gas –left side: 4 moles of gas; right side: 2 moles –↑ pressure causes shift to right If ↓ pressure, system shifts to side with more moles of gas –↓ pressure causes shift to left

H 2 (g) + I 2 (g)  2HI(g) this system has 2 moles gas on left & 2 moles gas on right systems with equal moles gas on each side cannot respond to pressure changes so NO shift occurs