Chemistry Equilibrium Test
I. Physical Equilibrium and Chemical Equilibrium (Physical refers to physical changes in reactions and chemical refers to chemical changes in reactions)
- Dynamic Equilibrium- when the rates of the forward and reverse reactions are equal. The system is dynamic because individual molecules react continuously
- Physical Equilibrium- very similar to chemical equilibrium, physical equilibrium does not involve any change in chemical properties.
- Chemical Equilibrium (Did not learn yet)- the state in which the chemical activities or concentrations of the reactants and products have no net change over time
- Reversible reactions can proceed in forward and reverse directions and don’t go to completion
- Reverse reaction is faster than forward reaction
- If concentration of products increase, the forward reaction is faster.
- If concentration of products decrease, the reverse reaction is faster
- At equilibrium, the concentrations of reactants and products are equivalent at constant.
- The concentrations of the reactants does not have to be the same as concentration of products.
II. Keq=CcDdAaBb when aA + bB cC + dD
III. Ksp=[A-]a[B+]when AaB aA + B
- Characteristics of Reversible Reactions:
- Products can react and form initial reactants
- Can never go to completion
- Natural processes. Spontaneous rxn
- Characteristics of Irreversible Reactions:
- Products cannot react and form initial reactants
- Can go to completion
- Does not occur on their own. Non-spontaneous rxn
- Rate of rxn= Change in concentration/ Time taken
- Rate of rxn is directly proportional to concentration of reactants
- Rate of forward reactions decreases as reactions progresses and rate of reverse reactions increases as reactions progresses.
- R of forward rxn= R of reverse rxn
- At equilibrium, K of forward rxn [A][B]= K of [C][C]
- Rxn doesn’t stop at equilibrium
- There is no change in concentration of reactants and products after equilibrium changed
- The value of the equilibrium constant or K depends only on temp. It changes when t changes.
- Rate of melting= Rate of freezing
- Rate of evaporation= Rate of condensation
- Rate of dissolving= Rate of crystallization
- [ ] is molar concentration= Molarity= moles/L
- Factors affecting Rate of rxn:
- Ionic substance react faster
- As energy increases, the number of collisions increases.
- As temp increases, there are more molecules required as there is more enrgy effective and collisions increases, faster rxn
- Pressure increases, more reactions
- Catalyst increases the rate by lowering the energy of activation.
IV. Collision Theory
· It states that reactions must have effective collisions with enough energy and proper orientation to react
V. Factors Affecting Rate of Reaction
· More exposure and surface area b/w reactants- more collisions
· Less space b/w molecules, more collisions
· Increased concentration, more collisions
· More average kinetic energy or temperature, then more collisions
· Catalyst causes proper orientation
- Pressure and temperature (only affects gas)
VI. Le Chatelier’s Principle
- If a system is at equilibrium and a stress is added or removed to the system, the equilibrium will shift to remove that stress.
IE: If a stress is added to the left, then equilibrium will shift to the right to balance out
- If concentration increases on left, shift goes to right
- For pressure, equilibrium balances by shifting to the side with the least moles. If both sides have the same number of moles, then changing pressure would have no effect.
- Concentration of reactants will decrease b/c they are used.
- Concentration of products will increase b/c they are formed
- Pressure doesn’t change concentration and effects only gases.
- Pressure increases when equilibrium shifts to the direction of less moles.
- If the reaction is exothermic, then the shift will be to the left. (Exothermic energy released --> warm) and prefer low temp
- If it is endothermic, the shift will be to the right.(Endothermic energy absorbed -->cold) and prefer high temp.
- Endothermic rxn rate increases by increase in temperature
- When temperature increases, the side with heat experienced more stress. Right side stress, left side shift
- Catalyst speeds up forward and reverse rxn equally and equilibrium reached faster.
- Common ion effect-a common ion from a different compound can shift the equilibrium
- In a thermochemical equation, the side that says heat is the side that experiences stress
VII. Colligative Properties
-Colligative properties-property of solvent that changes when solute is added to solution
-depends on number of particles
- Boiling point elevation and freezing point depression
- Molality= moles of solute/ Kg of solvent
Chemistry: Equilibrium
· Dynamic Equilibrium- when the rates of the forward and reverse reactions are equal. The system is dynamic because individual molecules react continuously
· Physical Equilibrium- very similar to chemical equilibrium, physical equilibrium does not involve any change in chemical properties.
· Chemical Equilibrium- the state in which the chemical activities or concentrations of the reactants and products have no net change over time
Reversible Processes
- Phase Changes Ex. H2O (l) à H2O (g)
- Solution Formation Ex. NaCl (s) à NaCl (aq)
- Reversible Reactions Ex. N2 (g) + 3H2 (g) ó 2NH3 (g)
A system comes to equilibrium when…
- The rates of the forward and reverse processes are equal
- The concentrations of the reactants and products are constant
The Law of Mass Action of aA + bB ó cC + dD
- Keq = [C]c[D]d / [A]a[B]b
- NOTE: only gases or aqueous species are included in the equilibrium constant (Keq)
- Keq changes with TEMPERATURE ONLY
The Equilibrium Quotient (Q)
- - [C]c[D]d / [A]a[B]b at ANY concentration
Le Chatelier’s Principle: If a system at equilibrium experiences a change in concentration, temperature, or pressure, the equilibrium position will shift to offset the change
RICE Charts
- R: Reaction
- I: Initial Concentration
- C: Change (negative on reactant side, positive on products side)
- E: Equilibrium
[Example] H2 (g) + I2 (g) ó 2HI (g), Keq = 64. Initial concentration: 0.2 M of H2 and I2, no HI
Ø R: H2 (g) + I2 (g) ó 2HI (g)
Ø I: 0.2 M 0.2 M 0
Ø C: – x – x + 2x
Ø E: (0.2 – x) (0.2 – x) (2x)
To solve for x:
Keq = [HI]2 / [H2][I2]
64 = (2x)2 / (0.2 – x)2
0.16 = x
Solubility Rules to Know
- All Group I cations are soluble
- All nitrates are soluble
- Halides with Ag. Pb, Hg2 are insoluble
- Common Ion: solubility is much less in the presence of a common ion
- Molar Solubility: concentration of ions in a saturated solution of a very insoluble compound
Ion Product (Q) and Solubility Product (Ksp)
- For AgCl (s) ó Ag+ (aq) + Cl- (aq) à [Ag+] [Cl-]
If…
- Q > Keq : too much products, the reaction will run in reverse
- Q < Keq : too much reactants, the reaction will run forward
- Q = Keq : AT EQUILIBRIUM
- K << 1 : reactants are favored
- K >> 1 : products are favored
- Reactant is added: shifts away fromP the added reactant (right)
- Product is removed: towards the removed reactant (right)
- Heat is added: away from the added heat
- Volume is decreased: pressure increases; shifts towards fewer moles of gases
- Q > Ksp : it will precipitate
- Q < Ksp : it will dissolve (unsaturated)
- Q = Ksp : at equilibrium (saturated)
- Ksp < 1 : very insoluble species
- Ksp > 1 : very soluble species
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