Chemical Equillibrium Flashcards
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 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-]
What does the value of the ionic product vary with?
tmeperature
What is the value of Kw at 25degreesC?
1x10^-14
What is the Brønsted-Lowry definition of a base and an acid
Base-proton acceptor
Acid-proton donator
What is there for every acid??
a conjugate base, formed by the loss (donation) of a proton
(loses H)
What is there for every base?
a conjugate acid, formed by the gain (accept) of a proton
(gains H)
What makes acids and bases strong?
they are completely dissociated into ions in aqueous solution
–>
Equilibrium lies (almost) completely to the right (lots of products)
100% of H+ or OH- ions to react at all times
What makes acids and bases weak?
they are only partially dissociated into ions in aqueous solution
<—>
Equilibrium lies (almost) completely to the right (lots of products)
Only a small proportion of H+ or OH- ions available
-ions react with another chemical and are removed from the equilibrium
-concentration of product is reduced
-equilibrium shifts to the right to replace ions
-more molecules dissociate to replace removed ions
-molecules will continue to dissociate to replace H+ ions as they continue to be removed by reacting
examples of strong acids
hydrochloric acid HCl
sulfuric acid H2SO4
nitric acid HNO3
examples of weak acids
ethanoic acid (carboxylic acids)
carbonic acid H2CO3
sulfurous acid H2SO3
example of a strong base
group 1 and 2 metal hydroxides
(except Mg)
examples of weak bases
ammonia and amines
How can the weakly nature of solutions of carboxylic acids, sulfur dioxide, and carbon dioxide be explained?
by reference to equations showing the equilibria
How can the weakly alkaline nature of a solution of ammonia or amines be explained?
by reference to an equation showing the equilibrium
Me formula for pure water
Kw=[H+][OH-]
What can Kw, the ionic product, be used to calculate?
pH values for strong acids and strong bases (since they dissociate fully into ions)
what is the pH?
potential of hydrogen ions
difference between monoprotic and diprotic?
what volume and concentration of HCl has the same neutralising ability as 50cm^3 of 1mol/l of H2SO4?
monoprotic
HCl and CH3COOH
1 H+ ion is released per molecule
diprotic
sulphuric acid
2 H+ ions released per molecule
100cm^3 of 1mol/l
