A2 Equilibria

Equilibrium= steady rate reached by a chemical reaction where foward and backward reactions both occur at equal rates.

HETERGENEOUS- different phases

HOMOGENEOUS- all the same phase

Le chatelier's principle- IF A REACTION IS AT EQUILIBRIUM AND REACTION CONDITIONS ARE CHANGES THE EQUILIBRIUM POSITION WILL MOVE IN THE DIRECTION WHICH OPPOSES THE APPLIED CHANGE.

• Write a balanced equilibrium equation
• use the equation the write the Kc expression
• if necessary calculate any unknown equilibrium concentrations using C-n/v
• substitute all known values
• calculate the unknown

REMEMBER- its always right over left

aA + bB---->. cC + d [D]

so Kc = [C]^c [D]^d

[A]^a [B]^b

ALWAYS REMEMBER UNITS (Mol/dm^3) and if there are no units write 'NO UNITS'

The Value of Kc is only Affected by A CHANGE IN TEMPERATURE

it is not affected by a change in CONCENTRATION

PRESSURE

OR BY ADDING A CATALYST

Equilibrium constants are normally expressed in terms of concentrations but for reactions involving gases we express the amount of gas in terms of partial pressure

PARTIAL PRESSURE =MOLE FRACTION X TOTAL PRESSURE

MOLE FRACTION IS FOUND USING THIS EQUATION

E.g the mole fraction of A in a mixture of A and B is;

Mole fraction of A=num of moles of A

Moles of A + moles of B