Equilibrium

Equilibrium

1. Kc

   • Units
     • Units of Kc  vary The equation is products/ reactants. Each concentration is moldm-3. the different concentration above and below cancel out to either get you moldm-3 (1 concentration as product left) dm3mol-1(1 concentration on the reacts is left) or none where concentration is equal for reactants and products.
   • Calculations
     • For the calculations, concentration of both the products and reactants needed. A titration and colorimeter are best.
   • [A] a x[B]b Products/ [C]c x [D]d reactants
     • Capital letters mean concentration. Lower case means the moles. Products/ reactants
     • To work out, first you need to make sure that you have a balanced equation. Then you work out the concentration during equilibrium. This is normally done by the moles given to you divided by the volume. The moles is the moles given in the balanced equation. Then you put the vaules in the formula
     • When you have to work out the moles. First right the first equation, where the reactants have values and the products are on zero. Write the next equation during equilibruim of the values you know. You should get an overlap of a concentration change. Find the difference, and all of the substance moles has changed by this. Then use appropertily. However be careful, this may only be the change for 1 moles, or 2, so divide to get one mole.
   • The meaning of the vaules
     • When Kc is 1, the postion of  equilibrium is inbetween reactants and products When Kc is above one, equilibrium is more to the products When Kc is below 1, equilibrium is more to reactants.

2. LA Chatelier

   • La Chatelier principle is that when in equilibrium there is a change such as temperature, pressure or concentration, then the system will to try to reduced this effect.

3. Kp

   • [pA] a x[pB]b Products/ [pC]c x [pD]d reactants
     • The same qualities as Kc however, partial pressure are used instead of concentration, which is similar equation to Kc but instead of moles parial pressure is used.

4. Definitions

   • Mole Fraction
     • This is  (Total number of moles in a component) / (total number of moles in a solution) When you add all the component of the same solution together you will get 1.
   • Partial Pressure
     • Partial pressure is the pressure of a gas in a mixture being the same amount if it was by itself in the same volume.
   • Partial Pressure=mole fraction x total pressure

5. Homogeneous and Heterogeneous equilibrium

   • Homogenous Reactions
     • This is where all the reactants and products are in the same state. This is the general equilibrium
   • Heterogeneous Reactions
     • This is where there are different states within the reaction (solid liquid gas) Important as the volume is constant in equilibrium, so solid and liquid do not change, therefore in Kc, the liquid and solid can be left out. e.g. P4(s)+5O2(g) <=>P4O10(s) Kc= [O2]5

6. Effecting K

   • Temperature
     • Increasing the temperature favours the endothermic reaction. This is because for an endothermic reaction, energy is absorbed from the surroidning in the form of heat. More energy favours the endothermic side, which is either the forward or backward reaction. depending on the reaction decreasing the temperature shifts equilibrium to the exothermic side
   • Concentration
     • Does not effect Kc This is because when you change the concentration, the reaction is no longer in equilibrium, so changes are made,(the concentration increases and decreases) which turns it back to the orginal Kc value.
   • Pressure
     • Does not effect Kc This is because when you change the pressure, the reaction is no longer in equilibrium, so changes are made,(the pressure increases and decreases) which turns it back to the orginal Kc value.
   • Catalyst
     • A catalyst does not effect the K, but does make the reaction faster in order to get to K. The forward and reaction would just occur quicker, hence canceling each other values out.