equilibria Flashcards
(24 cards)
what is a closed system?
no reactants or products can get in or out
what happens at dynamic equilibrium?
the rate of the forward reaction is the same as the reverse reaction when happening simultaneously, in a closed system
what are the two features of dynamic equilibrium?
-forward and backward reactions are occurring at equal rates
-the concentrations of reactants and products stay constant
what is le chatelier’s principle?
if the conditions of a reaction at equilibrium are changed, then the position of equilibrium moves to oppose that change
what is the effect of a catalyst on equilibrium?
a catalyst increases the rate of both the forward and reverse reactions equally
it does not change the position of equilibrium, but it reaches equilibrium faster
what happens to equilibrium when temperature is increased?
will shift to oppose increase in temp in the endothermic direction to try decrease temp
what will happen to equilibrium if temperature is decreased?
shift to oppose decrease in temp and will move in the exothermic direction to try and increase temp
how does equilibrium change when pressure is increased?
equilibrium will shift towards the side with fewer moles of gas to oppose the increase and thereby reduce the pressure
how does equilibrium change when pressure is decreased?
equilibrium shift towards the side with more moles of gas to oppose the decrease and thereby increase the pressure
if the number of moles of gas is the same on both sides of the equation, what effect will changing the pressure have on equilibrium?
no effect
what effect will increasing the concentration of reactants have on position of equilibrium and why?
equilibrium will shift to the right to use up added reactant and produce more product to oppose the increase in concentration
what effect will decreasing the concentration of reactants have on the position of equilibrium and why?
shifts to the left to oppose the decrease in conc, the backwards reaction will provide increase of the reactant concentration
what is Kc?
equilibrium constant
what does the c in Kc represent?
concentration
what is the equation for Kc?
[products]/ [reactants]
square brackets represent concentration in mol/dm3
indices of the brackets are the balancing numbers in front of each substance in the chemical equation
what is important to remember about the units of Kc?
they change depending on the equation
how do we work out moles of reactant at equilibrium?
initial moles- moles reacted
how do we work out moles of product at equilibrium?
initial moles + moles formed
explain how changing temperature affects Kc for an exothermic example?
raise temp;
-equilibrium shifts to the left to favour endothermic reaction to oppose the increase in temp
-more reactants formed so Kc gets smaller
opposite for if the temp is lowered
what effect does changing pressure or conc have on Kc?
NO CHANGE
if Kc is bigger than 1, what does this mean?
products rule and equilibrium must lie to the right
if Kc is smaller than 1, what does this mean?
reactants rule and equilibrium must lie to the left
what affect do catalysts have on Kc?
no effect on value of Kc because they have no effect on position of equilibrium
