equilibrium

• system


  the chemical reaction
• surroundings

  everything external to the system (e.g. temp)
• open system

  matter + energy exchanged w surroundings
• closed system

  only energy exchanged w system
• reversible

  products react again to reform original reactants (BOTH DIRECTIONS) [⇌]

  • e.g. most chem reactions, changing state
• irreversible

  products can't reform original reactants (ONE DIRECTION)

  • e.g. baking cake, combustion
• rate vs time graph

  • [reactants] ↓ , [products] ↑

  • products collide to reform reactants

  • eventually, forward and reverse reactions proceed at same rate → at EQUILIBRIUM

  • [reactants] + [products] remain constant
• concentration - time graph


  • products always start at 0M

  • ↑ [products], ↓ [reactants]

  • plateau = EQUILIBRIUM

  • change is based on the mole ratio
• dynamic state

  forward + reverse reactions occur concurrently at same time (not ceased)
• rate of reaction

  change in concentration of reactant or product over time (M/s)
• extent of reaction


  how far forward reaction proceeds before EQUILIBRIUM

  • not related to ROR

  • concentration of R + P are diff for diff equilibrium mixture
• equilibrium yield


  the amount of products present at EQUILIBRIUM relative to the amount of reactants
• 4 properties for equilibrium


  1. must occur in closed system

  2. rate of forward + reverse reactions are equal

  3. temperature + pressure are constant

  4. [products] and [reactants] are constant
• equilibrium law

  K = [PRODUCTS]/ [REACTANTS]

  • only in homogenous chem systems
  • units: P coeff - R coeff
• explaining equilibrium law

  Q < K → net forward reaction (right)

  Q = K → system at EQUILIBRIUM

  Q > K → net reverse reaction (left)
• equation reversed

  K inverted (reciprocal)
• equation doubled

  K squared
• equation halved

  K square rooted
• value of K : extent of reaction : relative concentration at equilibrium

  • less than 10^-4 : negligible : ↑ [reactants], ↓ [products]
  • b/w 10^-4 and 10^4 : significant: significant [reactants] and [products]
  • greater than 10^4 : almost complete : ↓ [reactants], ↑ [products]
  • greater or equal to 10^5 : complete : all reactants converted to products
• effect of change in temperature on endothermic reactions


  • energy ABSORBED from surroundings

  • favoured by ↑ in temp

  • ↑ temp = ↑ K ( F )

  • ↓ temp = ↓ K ( R )
• effect of change in temperature on exothermic reactions


  • energy RELEASED into surroundings

  • favoured by ↓ in temp

  • ↑ temp = ↓ K ( R )

  • ↓ temp = ↑ K ( F )
• Le Chatelier's Principle


  states “if a system at equilibrium is subjected to a change, the system will adjust itself to partially oppose the effect of the change”
• effect of position on equilibrium:

  temperature + EXOthermic reactions


  • this is an exothermic reaction

  • exothermic reactions are favoured by ↓ T → act to release energy into surroundings

  • ↓T (↓ energy in the surroundings) → causes net forward reaction to release energy (↑ K)

  • ↑T (↑ energy in the surroundings) → causes net reverse reaction to absorb energy (↓ K)
• effect of position on equilibrium:

  temperature + ENDOthermic reactions


  • this is an endothermic reaction

  • endothermic reactions are favoured by ↑ T → act to absorb energy from surroundings

  • ↑T (↑ energy in the surroundings) → causes net forward reaction to absorb energy (↑ K)

  • ↓T (↓ energy in the surroundings) → causes net reverse reaction to release energy (↓ K)
• effect of position on equilibrium:

  DILUTING solution by doubling volume of water


  • diluting solution by doubling volume of water = ↓ concentration of all species by 1/2

  • LCP states the system will act to partially oppose the change by ↑ concentration of the system

  • moves to side w most particles

  • net _____ reaction (depends on reaction)
• effect of position on equilibrium:

  DOUBLING VOLUME of container with a gaseous system


  • doubling volume of container = ↓ pressure of system by 1/2

  • ↓ concentration all species by 1/2

  • LCP states the system will act to partially oppose the change by ↑ pressure of the system

  • moves to side w most particles

  • net _____ reaction (depends on reaction)
• effect of position on equilibrium:

  HALVING VOLUME of container with a gaseous system


  • halving volume of container = ↑ pressure of system by double

  • ↑ concentration all species by double

  • LCP states the system will act to partially oppose the change by ↓ pressure of the system

  • moves to side w least particles

  • net _____ reaction (depends on reaction)
• effect of position on equilibrium:

  adding a CATALYST


  • catalysts ↓ Ea of forward + reverse reactions equally

  • ↑ rate of forward + reverse reactions equally

  • no change in [products] and [catalyst] or K or yield of products

  • no effect on position of equilibrium
• effect of position on equilibrium:

  adding an INERT GAS


  • inert gas ↑ total pressure of system

  • however, doesn’t change partial pressure of reactants + products

  • no change in [products] and [reactant] or K or yield of products

  • no effect on position of equilibrium
• effect on position at equilibrium:

  adding reactants 


  • adding reactant = ↑ concentration of reactant

  • sharp ↑ in concentration of reactant (on graph)

  • LCP states the system will act to partially oppose the change by ↓ concentration of reactant

  • net forward reaction
• effect on position at equilibrium:

  removing products 


  • removing products = ↓ concentration of product

  • sharp ↓ in concentration of reactant (on graph)

  • LCP states the system will act to partially oppose the change by ↑ concentration of product

  • net forward reaction
• effect on position at equilibrium:

  adding product 


  • adding product = ↑ concentration of product

  • sharp ↑ in concentration of product (on graph)

  • LCP states the system will act to partially oppose the change by ↓ concentration of product

  • net reverse reaction
• how to increase yield


  • ↑ temp for ENDOthermic, ↓ temp for EXOthermic

  • ↑ [reactants]

  • ↓ [products] - sell

  • ↑ pressure → less particles on product side

  • ↓ pressure → more particles on product side
• how to increase ROR


  • ↑ temp - $ + danger

  • ↓ volume = ↑ pressure of gas - $ + danger

  • ↑ concentration

  • ↑ SA of solid

  • add catalyst - $ + reuse
• yield


  theoretical: products expected if reactants fully react (stoichem)

  actual yield: mass of products actually obtained

  • slow ROR
  • reaches equilibrium
  • loss of substances during transfers

  % yield = (actual / theoretical) x 100