Model static and dynamic equilibrium and analyse the differences between open and closed systems

An open system can transfer both energy and matter with its surroundings.

A closed system can transfer energy in a form of heat or work but not matter with its surroundings.

  • A system that allows work but not heat to be transferred with its surroundings is an adiabatically isolated system.
  • A system that allows heat but not work to be transferred with its surroundings is a mechanically isolated system.

Static equilibrium – also called mechanical equilibrium, occurs when all particles in the reaction are at rest and there is no motion between reactants and products.  An example of static equilibrium is graphite turning into diamond which is an irreversible reaction.

Dynamic equilibrium – At dynamic equilibrium, reactants are converted to products and products are converted to reactants at an equal and constant rate.  A liquid and its vapor are in dynamic equilibrium when evaporation and condensation occur at equal rates.

Chemical equilibrium is an example of dynamic equilibrium in which the opposing processes are chemical reactions. Thermal decomposition of hydrated cobalt (II) chloride is under this type of equilibrium as well as the reaction between iron (III) nitrate and potassium thiocyanate.