1.6 Equilibria Flashcards
(13 cards)
Characteristics of equilibrium reactions
Rate of forwards reaction= rate of reverse reaction
Concentration of reactants and products remain constant
^^ MOST IMPORTANT
Dynamic- forwards and reverse reactions occurring at same time
Has to be a closed system (lid)
Define Le Chatelier’s Principle
If you subject and equilibrium reaction to change, it will move to oppose the change
Effect of concentration on equilibrium
Increase in conc of reactant- equilibrium moves to oppose increase in conc so moves to the other side
CONC DOES NOT AFFECT KC VALUES
Meaning of square brackets
Concentration is moles per dm cubed
Effect of pressure on equilibrium
Increase in P- equilibrium moves to oppose increase in P so moves to the side with less moles of gas
P DOES NOT AFFECT KC VALUES
Effect of a catalyst on equilibrium
Speeds up rate at which equilibrium is reached by providing alternative reaction route with a lower Ea and remaining chemically unchanged
No effect on position of equilibrium
Speeds up both forwards and reverse reactions EQUALLY
CATALYST DOES NOT AFFECT KC VALUES
Effect of temperature on equilibrium
If T increases, equilibrium moves to oppose increase in temp by moving in the endothermic direction
This lowers yield- need to compromise between yield and rate
T AFFECTS KC VALUES
How does T affect KC values?
If a reaction is endothermic in forwards direction then increasing T produces more products - higher Kc
If a reaction is exothermic in forwards directions then increasing T produces more reactants- lower Kc
How to get largest yield of ammonia?
Increase P (4 moles - 2 moles)
Increase conc of reactants and decrease conc of ammonia
Decrease T:
-because exothermic in forwards direction
-BUT although decreasing T gives a large yield, the reaction becomes v slow
-E of particles < Ea
-v few successful collisions in a unit of time
COMPROMISING:
- increase temperature to increase rate A BIT
-add a catalyst (Fe)
What does Kc equal?
Equilibrium constant expressed in concentration
-tells us whether and equilibrium reaction lies to RHS or LHS
Equation for Kc
Kc= conc of products/conc of reactants
Homogenous reactions
All substances in same state (aq)
What Kc values are good industrially and bad industrially?
10 to power of 10- more products- good
10 to power of -10- more reactants- bad
