Kc

• In an equilibria, it is very rare that the proportion of reactants and products is equal, equilibria only means the rate is the same
• The equilibrium constant represents the proportion of products compared to the reactants
• A high value of Kc (above 1) shows that the products predominate and the position of equilibrium lies to the right
• A small value of Kc (below 0) shows that the reactants predominate and the position of equilibrium lies to the left
• A homologous equilibrium is an equilibrium where everything is in the same state
• In a homologous equilibrium, we can work out Kc by constructing a Kc expression
• Kc uses concentration values
• [A] means 'concentration of A'
• If a compound has a coefficient, we must raise the compound to the power of the coefficient in the Kc experiment, to represent the number of times it appears (e.g 2H2 is represented in a Kc expression like: [H2]^2)
• A kc expression is concentration of products / concentration of reactants
• Units of a Kc expression vary due to the number of reactants/products varying
• To calculate Kc units, we can place moldm-3 in our K­C expression. Then we can cancel out the moldm-3s. When there are just units on either the numerator or denominator, we can multiply each unit, by adding the powers
• If the sum of the coefficients on the left hand side of the equation equals the sum of the coefficients on the right hand side, there are no units because they all cancel out
• To calculate equilibrium constant, you need equilibrium moles.
• The starting moles of each reactant and product and the equilibrium moles of one chemical are needed to calculate equilibrium moles.
• The change between the initial and equilibrium moles is calculated to find the equilibrium moles for each other chemical. If the change is negative on the left side, it will be positive on the right side
• If initial moles are not given for one side, they can be assumed to be all 0, indicating that the reaction has not yet begun.
• Only temperature changes the value of Kc