5) Unit 1 - Chemical Equilibrium Flashcards
when is a reaction said to be in equilibrium
when the rate of the forward reaction is equal to the rate of the of the backward reaction
name 3 things that alter the position of quilibrium
- altering the concentrations of products or reactants
- altering the temperature
- altering pressure when their are different number of moles on product and reactant sides
when writing the equilibrium constant K if there are pure solids or liquids what do you take their concentration as?
1
describe why altering concentrations of products or reactants does not affect K
- only affects the position of equilibrium but not K
- Adding more products will shift the equilibrium to the left. The system reacts to make more reactants therefore the ratio of products to reactants will be the same
describe why pressure does not effect k
- only affects the position and not the k value
- if pressure increases the equilibrium shifts to the side with the fewest gases moles
- therefore the equilibrium reacts to restore the same ratio as product to reactants
describe why changes in emperature does affect k
- K is temperature dependent
- if the forward reaction is endothermic, decreasing the temperature favours the formation of products
- If the forward reaction is endothermic, increases in temperature favours the formation of products
- Therefore the ratio of products to reactants is not the same as before, therefore altering the value of k
when would you use the ionic product of water.
•when you need to calculate the pH/pOH when given a concentration or pOH/pH of acid or base
what 2 formulas should you remember for the ionic product of water
H+ x OH- = 1x10-14
pH + pOH = 14
according to bronstead lowry’s definition of an acid and a base, what is an acid and what is a base
ACID = ELECTRON DONOR BASE = ELECTRON ACCEPTOR
what is a conjugate acid and a conjugate base
conjugate acid = species left when a base accepts an electron
conjugate base = species left when an acid donates an electron
strong acids and bases completely _______ in solution.
weak acids and bases partially _______ and form an _________ which lies mostly to the left.
strong acids and bases completely dissociates in solution.
weak acids and bases partially dissociate and form an equilibrium which lies mostly to the left.
what is the general Ka, for weak acids
ka = [H3O+][A-]/[HA]
the ______ the Ka, the stronger the acid
the ______ the pKA, the stronger the acid
the larger the ka, the stronger the acid
the smaller the pKa, the stronger the acid
formula used to work out the pH of a weak acid
pH = 1/2pKa - 1/2logc
what salt does a strong base and strong acid make and why
Neutral salt.
- Water exists in equilibrium producing H+ and Oh- ions.
- When the salt of a strong acid and strong base dissociates it will not react with the H+ or OH- ions in solution
- Therefore the concentrations of H+ and OH- are equal, making it neutral
what salt does a strong base and weak acid make and why
BASIC
- Water exists in equilibrium producing H+ and Oh- ions.
- When the salt of a weak acid and strong base dissociates, one of its ions will react H+, removing them out of the equilibrium
- This decreases the concentration of H+ in solution meaning OH-> H+. BASIC
what salt does a weak base and strong acid make and why
ACIDIC
- Water exists in equilibrium producing H+ and OH- ions
- When the salt of a strong acid and a weak base dissociates, OH ions are removed because one of the salts ions reacts with it
- This decreases the OH- ion concentration in solution meaning H+> OH. ACIDIC
indicators are usually weak acids?
true or false
true
what is the acid dissociation constant for an indicator ‘HIn’
Kin = [H3O+][In-]/[HIn]
the colour of the acid molecule HIn, is the same as the colour of the conjugate base in indicators.
True or false
false.
They are different colours
what formula is used to work out the pH of an indicator
pH = pKin + log[In-]/[HIn]
how much greater does the In- concentration have to be compared to the HIn, for colour to dominate (colour change)
10x greater
what is the equivalence point
the exact point when the exact amount of alkali has been added to neutralise an acid H+=OH-
what is a buffer solution
solution which the pH remains the same even on the addition of small amounts of acid or alkali or water.
What is an acid buffer
and give an example
solution of weak acid and one of its salt
e.g. sodium ethanoate and ethanoic acid
how do acid buffers work on the addition of H+
- H+ will react with the negative ion of dissociated salt
* the H+ are removed meaning the concentration of H+ remain the same
how do acid buffers work on the addition of OH-
- OH- will react with the H+ ion of the dissociated weak acid
- H+ ions will remain the same, because the equilibrium will react to produce more/ replace them from the large supply of the reactant (weak acid)
What is a basic buffer
and give an example
solution of weak base and one of its salts
e.g. ammonia solution and ammonium chloride
how do basic buffers work on the addition of H+
- H+ will react with OH- of dissociated weak acid
- OH- ions will remain the same, because the equilibrium will react to produce more / replace them from the large supply of the weak acid
how do basic buffers work on the addition of OH-
- OH- will react with the positive ion of the dissociated salt.
- The OH- ions are removed meaning the concentration of H+ and OH remain the same
one tip should use when calculating the pH of buffer solution
Put in the concentrations of acid and salt, in the NEW VOLUME. (x ratio stuff)
formula for calculating the pH of buffer solution
pH = pKa - log([acid]/[salt])
