5.1.2 - how far

• A reaction is at equilibrium when the rate of the forwards reaction equals the rate of the reverse reaction.
• To measure equilibrium you can:

  • measure change in colour using colorimeter
  • use ph probe
  • measure electrical conductivity
  • titration
• mole fraction is the amount of a given component in a given reaction mixture
• To calculate mole fraction:

  mole fraction = number of moles of A / total number of moles of all substances
• partial pressure is the pressure exerted by a single species in a reaction vessel
• symbol for partial pressure is P
• to calculate partial pressure:

  partial pressure = mole fraction x total pressure
• Relationship between concentration of a substance and its partial pressure is that the concentration of a substance is proportional to its partial pressure
• the two common units of pressure are

  pascals

  atmospheres
• For the reaction: aA + bB ——> cC + dD

  kp = pCcpDd / pAapBb
• to calculate units for Kp, write out the units for the partial pressures in the same arrangement for the Kp equation and cancel out the units.
• The symbol of the equilibrium constant is K
• when K is greater than 1:

  equilibrium lies to the right an the reaction favours the products
• when K is less than 1:

  Equilibrium lies to the left and the reaction favours the reactants
• increasing temperature means that equilibrium shifts to the direction of endothermic reaction
• decreasing temperature means that equilibrium shifts to the direction of the exothermic reaction
• the only factor that affects K is temperature
• if forward reaction is endothermic K increases as temperature increases
• if a forward reaction is exothermic K decreases as temperature increases
• Catalysts do not affect the position of equilibrium they only affect the rate of the reaction
• To convert the H+ concentration into pH:

  pH = -log[H+]
• to convert the pH into the H+ concentration:

  [H+] = 10^-pH
• pH scale is useful compared to [H+] because it allows a wide range of H+ concentration to be expressed simple positive values.
• a high pH means a small [H+]
• a low pH means a large [H+]
• if two solutions have a pH difference of 1 the difference in [H+] is a factor of 10
• [H+] of a strong acid = [HA]
• to calculate H+ concentration of weak acids:

  [H+] = square root (Ka x [HA])
• The assumption made when calculating the pH of weak acids is that it is assumed the concentrations of acid at equilibrium is equal to the concentration of acid after dissociation. This is because only very little of the acid dissociates.