Equilibrium constant

• The units for K_c vary and can be worked out from the equation.

• If the some of the equilibrium concentrations are known, the K_c expression can be rearranged to find the other equilibrium concentrations

Techniques and procedures to determine equilibrium constants

• Colorimetry

  • If one of the substance are coloured, a colorimeter can be used to measure the absorbance and a calibration curve used to find concentration

• pH

  • If one of the substances is an acid or a base, then a pH probe can be used to measure the pH and then pH calculations can be used to calculate concentrations

• Titrations cannot be used to determine equilibrium constants

  • This is because as the titrant reacts with the equilibrium mixture, the concentration of one of the substances will decrease and shift equilibrium to produce more of that substance

  • This continues until one side of the reaction has been used up