Equilibria

Equilibria

1. The idea of equilibrium

   • An equilibrium mixture is where you have a mixture of both reactants and products in a closed system. It has to be in a closed system to perform equilibrium as in a closed one when the products are formed they react and form the reactants again. Eventually the P and R are constant. Stoppered to prevent evaporation
   • Conditions for eqm = 1) can only be reached in a closed vessel, however it can take place in a beaker if the R and P are in a solvent. 2) can be approached from either direction and the final eqm will be the same as long as conditions of temp and pressure are the same. 3) it is a dynamic process so the rates of both reactions must be the same. 4) you know its been reached when the properties of the system dont change.
   • Chemical equilibria = A + B = C + D so we start with A and B only so the forward reaction occurs. C + D are being created, so now there is a reverse reaction as before there wasn't. Conc of A + B decrease so forward reaction slows down. When the same number of particles are being formed in AB CD then eqm has been reached

2. Changing conditions of eqm reaction

   • Le Chatelier's Principle = if a system at eqm is disturbed, the eqm moves in the direction that tends to reduce the disturbance
   • Concs = if A was increased in conc the eqm would move to the right to produce more C+D. If C was removed when it formed the eqm again would shift to the right
   • Pressure = only affect gases, eqm moves to the direction with fewer molecules to decrease the pressure or direction with higher molecules to increase the pressure if it was decreased
     • Lab example = N2O4 + 2NO2. Dinitrogen tetraoxide is a colourless gas and nitrogen dioxide is brown, set it up in a eqm in a syringe. If you decrease pressure by pulling out the syringe, the eqm moves to the right as the colour gets darker.
   • Temperature = if the reaction was exo in forward direction and temp was increased, eqm would move in the endo direction so to the left to cool down the reaction (endo absorbs heat)
   • Catalysts = no effect on eqm but they do allow eqm to be reached quicker so they are important in the industry

3. Industry

   • Using a high pressure is bad as it increases the costs of building the plant and energy costs running it. Low temp reduces reaction rate and so effects how fast eqm is reached. However, this can be counteracted by using a catalyst. If steam is used this can dilute the catalyst.

4. Effect of changing conditions on Kc

   • Temperature = Kc follows temp change in endothermic reactions but goes against change in exothermic reactions.
     • (1) Endo, temp decreases, Kc decreases, products decrease, reactants increase, eqm shits to left (2) Endo, temp increases, Kc decreases, P increases, R decrease, eqm shifts to right. (3) exo, temp increases, Kc decreases, P decreases, R increase, eqm shift to left. (4) Exo, temp decreases, Kc increases, P increase, R decrease, eqm moves right
   • Changing concentration = Kc does not change unless the temp changes. If you increase A eqm moves to the right, creating more product creating a new eqm with more product. This causes the top line of the eqm law expression to increase.
     • If Kc is more than 1, products predominate and eqm moves to right. If Kc is less than 1, reactants predominate and eqm moves to left
   • Catalysts = no effect on Kc and also eqm.