AS - Equilibria Flashcards
What happens before equilibrium is reached in a reversible reaction?
As the reactants get used up, the forward reaction slows down and as more product is formed, the reverse reaction speeds up.
What happens to a reversible reaction at equilibrium (dynamic equilibrium)?
The forward and reverse reactions proceed at equal rates and the concentrations of reactants and products remain constant.
A dynamic equilibrium can only happen in a what?
Closed system (where nothing can get in or out).
What is Le Chatelier’s principle?
If a reaction at equilibrium is subject to change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change.
What type of equilibria does Le Chatelier’s principle only apply to?
Homogenous equilibria (where every species of the reaction is in the same physical state).
Changing the pressure only affects equilibria involving what?
Gases.
How does increasing the concentration of a reactant affect the position of equilibrium?
The equilibrium will shift to the right to increase the concentration of product and oppose the increase of concentration of reactant.
What happens if the pressure of a gas equilibrium is increased?
The position of equilibrium shifts to the side with fewer Gad molecules to reduce the pressure and oppose the original increase in pressure.
What happens if you increase the temperature of an equilibrium?
The equilibrium shifts in the endothermic direction to absorb the additional heat and oppose the change.
What affect does a catalyst have on the position of equilibrium?
No effect on the position of equilibrium but they do mean that equilibrium is reached faster.
Why must a compromise of temperature and pressure be used for a reversible reaction used in industry?
Lower temperatures may increase the yield, but mean a slower rate of reaction.
High pressure may increase the yield of product, depending on the reaction, and speed up the rate of reaction, but high pressures are very expensive to produce.
Therefore, compromises must be used to produce an adequate yield at lower costs.
What is Kc and how is it deduced?
The equilibrium constant, deduced from the equation for a reversible reaction.
What does [X] mean?
The concentration of species X in mol dm-3.
Is the value of Kc affected by the addition of a catalyst?
No.
Why does changing the temperature change the value of Kc? How can you predict this change?
Because when you change the temperature, you also change the equilibrium concentrations of the products and reactants, so Kc will change.
You can predict this change:
If the temperature change means there’s more product at equilibrium, Kc will rise.
If the temperature change means there’s less product at equilibrium, Kc will decrease.
