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Equilibrium
4U Chem, incl acid and base equilib
| Question | Answer |
|---|---|
| equilibrium | when rate of the forward rxn = rate of the reverse rxn (because the concentrations are no longer changing) |
| Kc expression | Kc = k [products] / k [reactants] *each [ ] is raised to the power of coefficient in bal. eq. |
| value of Kc depends on: | temperature |
| favourable rxns are: | "downhill" or spontaneous |
| all favourable changes involve: | an increase in total entropy (randomness, disorder of energy in the universe) |
| equilibrium occurs when a system has reached: | maximum entropy |
| situations that increase entropy include: | Melting Vapourizing Making a sol’n Rxn forming inc # moles Heating a subst. |
| the value of Kc | tells the extent to which reactants have been converted to products. |
| If we had the K value 1.8x10^10 would products or reactants be favored at equilibrium? | products |
| small number for Kc | There isn’t much change in the initial [reactants ] so you can ignore -x in an ICE table |
| Le Chatelier's Principle | If we change the temperature, the pressure, or a concentration, the equilibrium shifts to reduce (or compensate for) that change |
| Q | Reaction quotient is calculated using concentrations that are not necessarily those at equilibrium |
| Q > Kc | reaction shifts left until Q=Kc (equilibrium) |
| In a bottle of pop, both the forward and backward reactions are occurring at the same time, we write: CO2(g) ⇌ CO2(aq) This is called: | dynamic equilibrium (changes at microscopic, not macroscopic scale) |
| different types of k values (all are constant at constant temp) | Keq (at equilibrium), Ka (for acids), Kb (for bases), Kw (for water), Ksp (solubility product constant) |
| PbCl2(s) ⇌ Pb2+ (aq) + 2Cl- (aq) What is the equilibrium expression: | K= [Pb2+][Cl-]^2 Remember that solids or liquids are never included in any K expression! |
| We use the Reaction Quotient (Q) | to determine how close we are to equilibrium conditions (at time, t) and which direction the reaction will shift. |
| N2 (g) + 3H2 (g) ⇌ 2NH3 (g) If pressure is increased, the equilibrium will want to shift to the side with | fewer moles (to the right) |
| N2 (g) + 3H2 (g) ⇌ 2NH3 (g) (ΔH = < 0) If heat is increased, the equilibrium will want to shift to the side with | to the left, to get rid of the excess heat |
| a saturated solution | is one that has the maximum quantity of solute dissolved. It is at this point that an equilibrium forms between the solid and the dissolved ions. Ex: AgCl(s) ⇌ Ag+(aq) + Cl-(aq) |
| Super saturated solution | the maximum amount of ions in solution is exceeded, precipitate will form (Qsp > Ksp) |
| common ion effect | describes the effect on an equilibrium when one or more species in the reaction is shared with another reaction. This results in shifting the equilibrium to the opposite side (to use up the excess). |
| for CdS(s) <--> Cd2+ (aq) + S2-(aq) adding a common ion | reduces the molar solubility and increases precipitation (shifts left) |
Created by:
jcepella
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