Chemical Equillibrium Flashcards
(41 cards)
When is a chemical reaction in equilibrium?
When the position of the reactants and products remains constant indefinitely.
What does the equilibrium constant K do?
Characterises the equilibrium composition of the reaction mixture.
What is the general reaction, aA+bB -> cC+dD, equilibrium expression?
K = [C]^c [D]^d / [A]^a [B]^b
what are
1.[A] [B] [C] [D]
2.a b c d
- Equilibrium concentrations of A B C D
- The stoichiometric coefficients in the balanced reaction equation
What does the equilibrium constant indicate?
the position of equilibrium
What value of concentrations are pure liquids and pure solids given in the equilibrium expression
taken as constant = 1
What is the (numerical value of) equilibrium constant dependant on?
reaction temperature
What is the (numerical value of) equilibrium constant independant of?
concentration and/or pressure
For endothermic reactions, what happens to the K value and yield of products if the temperature is increased?
increase in K
increase in yield of product
For exothermic reactions, what happens to the K value and yield of products if the temperature is increased?
decrease in K
decrease in yield of product
What does le Chatellier’s principle state?
If any changes are applied to a reaction at equilibrium, the position of equilibrium will shift to try and minimise the change
(an system at equilibrium will counteract an applied change)
Where can an equilibrium be established
only in a closed system
What does a high K mean? (above 1)
higher percent of products in equilibrium mixture
What does a low K mean? (below 1)
lower percentage of products in equilibrium mixture
What is homogeneous equilibrium?
when all species are in the same state
What is heterogeneous equilibrium?
It has species that are in more than one state
What happens when concentration is changed in an equilibrium and why?
The value of K remains constant (at the same temp) as the equilibrium position shifts which results in changes in the concentrations of the species in the reaction
Effect of a catalyst on an equilibrium?
-lowers activation energy for both forwards and reverse reactions by the same amount
-no change in the equilibrium concentration so position of equilibrium remains unchanged
-catalysts speed up the rate at which equilibrium is established
What does K NOT indicate?
the rate at which dynamic equilibrium is established
In water and aqueous solutions, what is there an equilibrium between?
the water molecules + hydronium (hydrogen) and hydroxide ions
Ionisation of water formula
H2O (l) + H2O (l) <> H3O+ (aq) + OH- (aq)
H2O = acid
H2O = base
H3O+ = conjugate acid
OH- = conjugate base
what does H3O+ represent?
a hydronium ion/hydrated proton
( H+ in shorthand)
What is one word to describe water and what does it mean?
amphoteric-can react as an acid and a base
What is the dissociation constant for the ionisation of water known as? (+what is it represented by+formula)
the ionic product and is represent by Kw
Kw=[H3O+][OH-]
