Equilibria. Flashcards
Conditions in an equilibrium system.
Rate of forward reaction is equal to the rate of the reverse reaction.
The concentrations of reactants and products do not change.
Both reactions are taking place.
System must be closed.
La chatelier’s principle.
When a system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change.
Effect of change of concentration.
Increase in concentration of reactants=equilibrium shifts to right to use up reactants.
Decrease=shifts to the left to make more reactants.
Same rule applies for inc/dec in products but shifts left for reverse reaction.
Effect of change in temperature.
Increase in temperature=equilibrium shifts to favour the endothermic reaction(delta H is positive), right if endothermic is forward, to take heat energy in and reduce affect of increase.
Decrease in temperature=equilibrium shifts to favour exothermic reaction(delta H is negative).
Effect of change in pressure.
Increase in pressure of system=equilibrium will shift to side of reaction w/ fewer molecules to minimise pressure increase of system as reduces number of gaseous molecules.
Decrease does opposite to equilibrium.
Effect of a catalyst on equilibrium.
Does not change position of equilibrium.
Speeds up rate of forward and reverse reactions equally.
Increases the rate at which equilibrium is established.
Formula for Kc/equilibrium constant.
products/reactants
where all products are multiplied on top
and the number of moles becomes a power to the bracket of the substance.
Use given equilibrium concentrations to sub in for the substances in the Kc equation.
Have to use same equation to calculate units w/ moldm^-3.
Interpretation of Kc constant.
1=position of equilibrium is halfway between products and reactants
Kc>1 indicates equilibrium position is towards products
Kc<1 indicates equilibrium position is towards the reactants.
