Wine Analysis
Kinetics
- Kinetics refers to the energy, activity, movement, motive force or physical and chemical dynamics of a given situation.
- The equilibrium of a chemical reaction is very much dependent on the kinetics of the species involved.
- As and example, common salt, sodium chloride (NaCl) disassociates in water (aq) into sodium ions (Na+) and chloride ions (Cl-) as per the equation below.
NaCl (aq) <=> Na+ (aq) + Cl -(aq)
- The double headed arrow indicates that the reaction can proceed in either direction and that even at equilibrium NaCl is disassociating and Cl - and Na+ are re-associating at the same time, however at a constant rate , maintaining constant concentrations of the species involved.
- These concentration ratios can be calculated as a constant, (a dissociation constant in this case), at a specified temperature and pressure.
- The association/dissociation reactions of NaCl is dependent on the strength of the ionic bond between Cl - and Na+ offering resistance to the solvent action of water
It is also dependent on the amount of kinetic energy the species possess, as an increase in their kinetic energy increases the number of collisions encountered between them - note a minimum quantity of kinetic energy, together with the correct orientation of the molecules to each other is required for bonding or dissociation to occur.
- A change in temperature can also affect the concentration ratios by affecting the kinetic energy and the overall energy state of the reaction.
- An increase or decrease in any of the species' concentrations will alter the ratio of collisions and reactions between them until the ratio of concentrations for the species involved are reestablished.
That is the. addition of either Na+ or Cl - to the equation below will see the reaction proceed to the left to reestablish the concentration ratio of the species as determined by its dissociation constant at equilibrium.
Similarly the addition of NaCl will see the reaction proceed to the right
NaCl (aq) => Na+ (aq) + Cl -(aq)
until an equilibriunm situation is reestablished.
NaCl (aq) <=> Na+ (aq) + Cl -(aq)
Note: When all water molecules present are used to surround (solvate ) the Na+ or Cl - present, any further additions of NaCl will not result in any further dissociations and exist as solid NaCl in solution, at that temperature. The solution is then said to be supersaturated.