AQA A level Chemistry Equilibria with correct answers

What are the four conditions that apply to all equilibria? 1. Equilibrium can only be reached in a closed system 2. Equilibrium can be approached from either direction and the final position will be the same 3. Equilibrium is a dynamic process. It is reached when the rates of the two opposing processes are the same. 4. We know equilibrium is reached when the macroscopic properties of the system do not change with time (density, concentration, colour and pressure) What is Le Chatelier's principle? If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance. 00:10 01:36 What happens when we increase the concentration of one of the reactants? The equilibrium shifts to oppose the change in concentration, usually by making the reactant react more in order to reduce its concentration. What happens when we change the overall pressure? The equilibrium shifts to the side with fewer moles to oppose the change in pressure. What happens when we increase the temperature of an equilibrium? The equilibrium will shift in the endothermic direction in order to oppose the increase in temperature. Do catalyst have an effect on the position of the equilibrium? No, catalyst effect both the forward and backwards reaction equally. What is Kc? The equilibrium constant How will increasing the temperature effect Kc? Endothermic: increase Exothermic: decrease How will decreasing the temperature effect Kc? Endothermic: decrease Exothermic: increase Does concentration effect Kc? No If Kc is much greater than 1 then what is predominant and causes the equilibrium position to be over to the right? Products predominate over reactants If Kc is much less than 1 then what is predominant and causes the equilibrium position to be over to the left? Reactants predominate over products