ES 4- Chemical Equilibrium Flashcards
Define dynamic equilibrium
Reaction has reached overall stage of balance, but forward and reverse reactions are still occurring at same rate. No overall change
Describe changes in macroscopic and microscopic characteristics of a action one equilibrium is reached
Macroscopic- no change (colour, volume etc)
Microscopic- constantly changing
Give exam style answer of what is occuring when reaction has reached chemical equilibrium
- conc of reactants and products are constant
- forward and reverse reactions are both happening
- rate of reactions are the same
What happens to conc of reactants when reaching equilibrium?
- conc decreases, as it is converted to products
- eventually becomes constant
What happens to conc of products when reaching equilibrium
- conc increases, as forward reaction progresses
Eventually becomes constant
Describe how rate of reaction changes when reaching equilibrium
- rate of forward reaction starts rapidly, then decreases as conc decreases (less successful collisions), becomes constant
- rate of reverse reaction starts slowly due to low conc of products, speeds up and eventually becomes constant
What is Kc?
Ratio of reactants to products at chemical equilibrium
What is Kc affected by?
Temperature
Give expression for Kc
Kc=(C)c x (D)d
(A)a x (B)b
How do you calculate units for Kc?
Powers cancel on top and bottom halves of expression, use indices rules
If Kc is larger than 1…
More products than reactants at equilibrium
If Kc is less than 1…
More reactants than products at equilibrium
Give Le Chatelier’s principle
‘If dynamic equilibrium is disturbed by changing conditions, the position of equilibrium moves to counteract this change’
If a change to conditions results in less product being made, what needs to happen for Kc to stay constant?
Bottom half of expression (reactants) must decrease to counteract change
When conc of reactants is increased, position of equilibrium shifts…
Right towards product, conc of products increases
