Equilibria Flashcards
What is an equilibrium mixture?
The mixture of reactants and products formed when a reversible reaction is allowed to proceed in a closed container until no further change occurs. The forward and backward reactions are still proceeding but at the same rate.
What is a dynamic equilibrium?
A situation in which the composition of a constant concentration reaction mixture does not change because both the forward and backward reactions are proceeding at the same rate.
Conditions for equilibrium
It can only be reached in a closed system (where the products and reactants cannot escape). It can be approached from either direction and the final equilibrium position will be the same (as long as physical conditions don’t change). It is a dynamic process (reached when the rates of two opposing processes are the same). It has been reached when the macroscopic properties of the system don’t change with time.
Le Châtelier’s principle
If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance.
What happens if you increase the concentration of one reactant for a system in equilibrium?
The equilibrium will shift in the direction that tends to reduce the concentration of this reactant. It increases the yield of products.
What happens if you increase the pressure of the system in equilibrium?
The position of equilibrium will move to decrease the pressure by favouring the reaction that forms fewer gas molecules.
What happens if you increase the temperature of a system in equilibrium?
The equilibrium moves in the direction that cools the system down so favours the endothermic reaction.
What effect do catalysts have on equilibrium?
No effect on the position as it affects the forward and backward reactions equally by producing an alternative route for the reaction with a lower activation energy. However, they do allow equilibrium to be reached more quickly.
What is Kc and how do you find it?
The equilibrium constant (of concentration). You do the concentrations of the products multiplied together over the concentration of reactants multiplied together. Each species is in square brackets and to the power of its coefficient (outside the brackets). It applies in a homogenous equilibrium. Has variable units. Only affected by concentration and temperature so temp should be stated.
How to use moles to find Kc
Write down the initial moles of each species given in the question. Find the change in moles to equilibrium position. Use this to find the increase or decrease in moles of other species. Write down the moles at equilibrium. Use the volume of the container to find the concentration (or use V if not given) and then do the normal thing to get to Kc.
