1.06 Equilibria

• Define the term 'dynamic equilibrium'


  The rate of forward reaction is equal to the rate of reverse reaction

  • Hence, the concentrations of reactant and product do not change
• Give essential conditions for an equilibrium mixture.


  • Equilibrium occurs in a closed system (where reactants and products cannot escape)
  • Macroscopic properties (volume, concentration, etc.) do not change with time
• State Le Chatelier's principle.

  If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance.
• In the equation $CH_{4\left(g\right)}+$$H_2O_{\left(g\right)}⇌\ CO_{2\left(g\right)}+$$3H_{2\left(g\right)}$, with enthalpy change of +210kJmol-1, what effect would increased temp. have on the position of equlibrium?


  Equilibrium position shifts to the right

  • This is because the forwards reaction is endothermic due to the positive enthalpy change, therefore yield of hydrogen increases
• In the equation $CH_{4\left(g\right)}+$$H_2O_{\left(g\right)}⇌\ CO_{\left(g\right)}+$$3H_{2\left(g\right)}$, with enthalpy change of +210kJmol-1, what effect would increased pressure have on the position of equilibrium?


  The equilibrium shifts to the left

  • This is because the forward reaction produces more moles of gas than the reverse reaction (4 moles product, 2 moles reactant) therefore yield of hydrogen decreases
• In the reaction $CH_{4\left(g\right)}+$$H_2O_{\left(g\right)}⇌\ CO_{\left(g\right)}+$$3H_{2\left(g\right)}$, suggest and explain why an industrial chemist may use a high pressure for this production of hydrogen?


  • High pressure increases the collision frequency, increasing the rate of reaction
  • This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen
• What effect does a catalyst have on the position of equilibrium?


  No effect

  • Because catalysts affect rate of forward and reverse reactions equally
• What conditions affect the value of Kc (equlibrium constant) out of concentration, catalyst, pressure or temperature?


  Temperature
• What type of system is Kc relevant for

  Homogenous systems in equilibrium
• What does Kc being greater or lesser than 1 suggest for the position of equilibrium?


  • Greater than 1 = over to the right
  • Lesser than 1 = over to the left
• What effect does decreasing the temperature in an endothermic reaction have on Kc?

  Kc decreases
• What does increasing the temperature in an endothermic reaction have on Kc?

  Kc increases
• What effect does decreasing the temperature in an exothermic reaction have on Kc?

  Kc increases
• What effect does increasing the temperature in an exothermic reaction have on Kc?

  Kc decreases