TOPIC 10-EQUILIBRIUM 1

• Dynamic equilibrium occurs when:

  1. Forward and backward reactions are occurring at equal rates.
  2. Rate of forward and reaction is equal to the rate of backward reaction.
  3. The concentrations of reactants and products stays constant (do not change with TIME)
  4. Conditions required for equilibrium:

  • reactions must be reversible and in a closed system
• remember: products goes up, reactants goes down

  A) constant

  
• CONCENTRATION AND TIME GRAPHS

  reactions from reactants to products: reactants goes down, products goes up AND MEET LINES

  reactions from product to reactants: product goes down, reactants goes up

  A) directions

  
• RATE AND TIME GRAPHSin the first graph, rate of forward and backward reactions are the same/equalin the second graph,

  forward reaction: initially reactants are used up quickly but then slow as their conc drops.

  backward reaction: initially reactants are reformed slowly but then speed up as the conc of products increases

  A) equal

  B) no change

  
• Le Chatelier’s principle - if a reaction at dynamic equilibrium is subjected to a change (in pressure, conc, temp), the position of equilibrium will shift to counteract this change.
• Le Chatelier's Principle - CHANGING TEMPERATURE

  increasing temp.... increases the rate of both forward and backward reactions BUT the endothermic reaction rate increases more than the exo rate so that equilibrium will shift in the endo side.
• Le Chatelier's principle - CHANGING TEMPERATURE

  e.g. if delta H= -ve , it means that FORWARD REACTION is EXO.

  if we increase temp, eqm will shift in endo direction (to the left) to reduce the temp. so more N2 and H2 will be produced.

  if we decrease temp, eqm shifts to right, so more 2NH3.

  A) shift

  B) endo

  C) decreased

  D) exo

  E) heat

  F) higher

  G) slow

  H) compromise

  I) shift

  J) endo

  K) decrease

  L) left

  M) lower

  
• LE CHATELIER'S PRINCIPLE - CHANGING TEMPERATURE

  if FORWARD reaction is ENDO: when delta temp is +ve

  • increasing temp will move eqm to right (products)
  • decreasing temp will move eqm to left (reactants)

  
• LE CHATELIER'S - Effect of pressure on equilibrium

  Increasing pressure will cause the eqm to shift towards the side with FEWER MOLES of gas to oppose the change and reduce the pressure.

  A) no effect

  B) position

  C) higher

  D) faster

  E) expensive

  F) energy costs

  G) fewer

  H) right

  I) higher

  
• LE CHATELIER'S - CHANGING CONCENTRATION

  e.g. adding more BiCl3 will shift to the right

  removing BiCl3 will shift to the left

  A) right

  B) left

  C) uses up

  
• LE CHATELIER'S- Effect of Catalysts on Equilibrium

  • NO effect on the position of equilibrium, but speeds up the rate of equilibrium so is reached more quickly. NO effect on yield.
  • increases/speeds up the rates of both the forward and backward reactions by the same amount
• LE CHATELIER'S - CHANGING CONC

  • adding H+ ---- by adding an acid
  • add OH- ---- by adding a base to react and remove H+ from eqm

  A) right

  B) orange

  C) reacts

  D) removes

  E) left

  F) yellow

  
• LE CHATELIER'S - EFFECT OF PRESSURE ON YIELD

  !! pressure only has an effect if there's a diff in moles in both sides

  !! no effect on yield but as pressure increases, rate of reaction increases

  A) no effetc

  B) pressure

  C) increases

  
• change in temp is endo bc +ve.

  • removing H2(g) , increases the yield of CO bc eqm to the right bc goes to theo ne with more H+

  A) decrease

  
• forward reaction is exo bc change in temp is -ve

  • lowering the pressure has no effect on yield of CO2 BUT ON THE RATE

  A) increase

  B) the same

  
• LE CHATELIER'S - effect of temp/ pressure

  A) temperature

  B) pressure

  C) exo

  D) left

  E) fewer

  F) right

  G) left

  H) greater

  
• C(graphite)= C(diamond). change in temp=+1.8 Kj mol-1 SO ENDO

  density= 2.3 g cm-3 density= 3.5 g cm-3

  suggest the conditions of temperature and pressure that would favour the fomation of diamond, justify.

  • high temp bc forward reaction is endo.
  • distance btw layers in graphite are higher than C-C bonds in lenght.
  • so, in diamond there are more matter (C-C atoms are packed more closely together) in a given volume. --- so , high pressure is vavoured
• which allotrope is more thermodynamically stable?

  • graphite bc it's a lower energy.

  are diamonds forever?

  • no bc activation energy is too high. so, diamond doesn't turn into graphite.

  A) graphite

  
• as temp increases, % yield of ammonia decreases. so, forward reaction is exo, eqm shifts to the left

  A) temperature

  B) decreases

  C) exo

  
• what conditions of temperature and pressure will give a maximum yield of ammonia?

  • low temp bc forward reaction is exo.
  • high pressure bc there are 2 moles of gas on the right and 4 on the left

  
• LE CHATELIER'S Q- TEMPERATURE

  compromise: 450° c

  A) higher

  B) faster

  C) efficiently

  
• LE CHATELIER'S Q- PRESSURE

  A) increases

  B) yield

  
• LE CHATELIER'S Q

  A) exo

  B) increases

  C) decreases

  
• LE CHATELIER'S Q- PRESSURE

  • high pressure, increase the yield of SO3 and rate.
  • the pressure used is 2 atm bc yield is already high at 1 atm

  
• LE CHATELIER'S CONDITIONS (COMPROMISED)

  • Low temp gives good yield but slow rate: compromise temp used
  • High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure and too high equipment costs
  • catalysts speed up the rate allowing lower temp to be used (and hence lower energy costs) but have no effect on eqm
  • Recycling unreacted reactants back into the reactor can improve the overall yields of all these processes
• HOMOGENEOUS EQUILIBRIA - A system in which all components are in the same phase e.g. H2(g) + I2 (g)---- 2HI(g)

  HETEROGENEOUS EQUILIBRIA- A system where at least 2 different phases are present e.g. CaCO3 (s) ---- CaO (s) + CO2 (g)
• SOLIDS AND LIQUIDS DO NOT APPEAR IN THE EQM REACTION/FORMULA

  A) solids

  B) constant

  
• Effect of changing conditions on value of Kc

  • The larger the Kc the greater the amount of products. If Kc is small we say the equilibrium favours the reactants
  • Kc only changes with temperature. It does not change if pressure or concentration is altered. A catalyst also has no effect on Kc

  
• 2nd equation - is half of the first one

  3rd - is the reverse of the first one

  A) -1/2

  B) 3/2

  
• LE CHATELIER'S - EFFECT OF CATALYST ON EQM/ Kc value

  Catalysts speeds up the rate allowing lower temperatures to be used (and hence lower energy costs) but have no effect on equilibrium.

  A) no effect

  B) speeds

  C) rate

  
• QUESTION- calculate the conc of water.

  imagine the water density= 1 g cm-3

  conc = 10^3 g/18 g mol-1 / 1 dm3= 55.6 mol dm-3
• H2O in eqm expressions

  • water doesn't appear in the equation if its the solvent, so if an aqueous product is formed.

  A) not the solvent

  
• WHAT AFFECTS Kp?

  A) pressure

  B) Kp

  C) increase

  D) decrease