 Equilibrium is reached in a closed system when the rates of the forward and the backward reaction are equal.  The Equilibrium law describes how the equilibrium constant (K c ) can be determined for a particular chemical equation.  The magnitude of the equilibrium constant indicates the extent of a reaction at equilibrium and is temperature dependent.  The reaction quotient(Q) measures relative amount of product and reactants present during a reaction at a particular point in time.  Q is the equilibrium expression with non-equilibrium concentrations. This changes with changes in concentration, pressure, and temperature.  A catalyst has no effect on the position of equilibrium of the equilibrium constant.

 In a ‘traditional’ reaction, all the reactants get turned into products (assuming no excess)  In an equilibrium reaction this is not the case, and the reaction sort of ‘stops’ part way through REACTANTSPRODUCTS ‘TRADITIONAL’ EQUILIBRIUM

 Equilibrium reactions are written using a double arrow  Each of the arrows only has a single-sided head  The unit will make a lot of reference to the rate of the:  ‘forward reaction’ (reactants becoming products)  ‘back reaction’ (products becoming reactants) REACTANTSPRODUCTS

 The concentration of reactants and products is constant  They are NOT equal to each other  They are just not changing  The rate of the forward reaction is equal to the rate of the back reaction  At equilibrium these are not zero…even though it looks like it on the graph

 The reaction hasn’t stopped, it is still going, but the rate of the forward and back reactions are equal, so there is no overall change.  This is different to a static equilibrium (for example a see-saw) where there is no change at all.

 The equilibrium constant describes where the position of equilibrium lies:  Minimum: 0, maximum: ∞, half-way: 1  Greater than 1: products favoured  Less than 1: reactants favoured  For the reaction: wA + xB ⇌ yC + zD

 Complete the paper equilibrium activity.paper equilibrium activity  Record your observations in a table like this: StepWhite squares Black squares Forward rate Backward rate Equilibrium constant 01000n/a ∞ 1 2 …