Topic: EQUILIBRIUM Do Now:

VIDEO CLIP

Equilibrium = Balance Not necessarily equal 1 man and 1 man equal but not balanced

BALANCED!

Chemical equilibrium Rate of forward reaction is EQUAL to the Rate of the reverse reaction Concentrations are not necessarily equal but they are constant, unchanging

Time Concentration NH 3 H2H2 N2N2 N 2 (g) + 3H 2 (g)  2NH 3 (g) EQUILIBRIUM POINT

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

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 Liquid – Vapor Equilibrium NOTE: anytime a gas is involved, the container must be sealed for equilibrium to be reached- if not the gas will escape!

Solution Equilibrium –saturated solution with some solid on the bottom of the container. As one molecule dissolves, one molecule precipitates (forms solid). –Ex: Too much sugar in the coffee. - EX: CO 2 in water CO 2 (g)  CO 2 (aq) favored by high pressure & low temperature

Reversible Reactions Most chemical reactions are reversible. Reactants react to form Products, then the Products react to form Reactants. N 2(g) + 3H 2 (g)  2NH 3(g) N 2 reacts with H 2 to form NH 3 at the same time, NH 3 is consumed and forms N 2 and H 2

Reversible Rxn vs Reaction that goes to completion NaOH + HCl --> NaCl + H 2 O

equilibrium can be changed or affected changes in concentration, pressure, temperature affect forward & reverse reactions differently composition of equilibrium mixture will shift to accommodate these changes

Le Chatelier’s Principle When a system at equilibrium is subjected to a stress, the equilibrium will shift in the direction which tends to relieve the stress. –stress = change in concentration, volume, pressure, or temperature

Increase Concentration INCREASING the concentration causes the equilibrium to shift AWAY from the substance that was added.

N 2 + 3H 2  2NH 3 Increase N 2 At equilibrium In order to get back to equilibrium, what has to happen? Need more products! What happens to the amount of H 2 ? Rxn shift to the RIGHT

N 2 + 3H 2  2NH 3 Increase NH 3 Need more N 2 and H 2 so reaction shifts to the left

DECREASING the concentration causes the equilibrium to shift TOWARD the substance that was removed.

N 2 + 3H 2  2NH 3 Decrease NH 3 Need more NH 3 so reaction shifts to the right

Changes in Temp exothermic reaction: A + B  C + D + heat consume –If ↑ temperature, system shifts to consume heat so shifts to left  –so endothermic rxn favored endothermic reaction: A + B + heat  C + D –If ↑ temperature, system shifts to consume heat so shifts to right –so exothermic rxn favored shift in the direction opposite of the “heat” term

!! PRESSURE !! Increase PRESSURE, shift toward the side of the equation that has LESS MOLES of GAS. Decrease Pressure, shift toward the side of the equation that has MORE MOLES of GAS. N 2 (g) + 3H 2 (g)  2NH 3 (g)

VOLUME Increasing Volume decreases pressure. Equilibrium will shift toward greater number of moles of gas. Decreasing Volume increases pressure. Equilibrium will shift toward smaller number of moles of gas.

Reactions that go to completion – equilibrium can not exist Formation of a gas which escapes H 2 CO 3 (aq)  CO 2 (g) + H 2 O (l) Formation of water HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) Formation of a precipitate (insoluble compound) NaCl (aq) + AgNO 3 (aq)  AgCl (s) + NaNO 3 (aq)

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