equillibria + acid base Flashcards
what is Le Chatelier’s principle
if a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will move to counteract the change
what happens if you increase conc in homogenous reversible reaction
equillibrium will shift to try and reduce the conc (use up the increased conc)
what happens if you increase pressure in homogenous reversible reaction
equilibrium will shift to try and reduce the pressure (shifts to side with fewest number of gas particles)
what happens when you increase the temp in homogenous reversible reaction
equilibrium shifts to endothermic direction to reduce temp
conditions for making ethanol
60atm pressure
300C temperature
phosphoric acid catalyst, H3PO4
what is dynamic equilibrium
when both the rate of the forward and backward reaction are equal, the conc of reactants and products remain constant
what do catalysts do to equilibrium
they affect forward and backward reaction equally, allowing equilibrium to be reached faster
what states do we use in Kc expressions
aqueous + gases
only in homogenous equillibria
what is the one thing that affects Kc
if temperature changes
if anything else shifts equillibria the conc of reactants and products stay in same ratio
why does changing the concentration of a species not affect Kc
increasing 1 species will shift equilibrium to restore the conc to be proportional so same ratio of reactants and products are still in equilibrium
how to work out Kc in opposite direction
1/ Kc for other reaction
what is the partial pressure of a gas
the pressure the gas would exert if it alone occupied the volume of the mixture
in exothermic reaction what happens to Kc/Kp when temp is increased
become smaller as position of equilibrium moves to the left so less products over reactants
why do catalysts not affect Kp or Kc
they affect the rate of reaction but not the position of equilibrium, so they are only affecting how fast the system reaches equilibrium
what is a Bronsted Lowry base
proton acceptor
what is a Bronsted Lowry acid
proton donor
is a Bronsted Lowry conjugate acid positive / negative
positive, accepts protons
is a Bronsted Lowry conjugate base positive / negative
negative, donates protons
define pH
-log H+ concentration
what is a strong acid
an acid that completely dissociates into ions in a solution, releasing the greatest number of hydrogen ions
what is a weak acid
an acid that only partially dissociates in water to produce hydrogen ions
define the ionic product of water Kw
the product of the molar concentrations of hydrogen ions and hydroxide ions in water at a specific temperature
define pKa
-log Ka
what does buffer solution mean
a solution that resists changes in pH when small volumes of an acid or base is added to it
explain the use of blood being a buffer
carbon dioxide dissolved in the blood forms carbonic acid
so carbonic acid will shift right forming more H+ and hydrogencarbonate ions
large reservoir of hydrogencarbonate ions will react with H+ to restore pH
why is the enthalpy of neutralisation less for weak acids
only partially dissociate/ionise
some H+ are not free to react with OH- ions
why are solids and liquids not in Kc expression
we assume that their concentrations remain constant
whats total pressure
sum of all the pressures of the individual gases
what affect does changing temperature have on Kp
if temperature change causes equilibrium to shift right then Kp will increase
what is a polyprotic acid
an acid that donates more than one proton eg sulfuric
why does H2O cancel out of Kw expression
we assume the conc of water remains constant as dissociates very weakly
how do you calibrate pH meter
put it in distilled water, should read 7.0
repeat process with standard solutions of pH 4.0 and pH 10.0, rinse probe between them with water
what assumptions do we make about weak acids and H+ in Ka expression
moles of HA at start = moles of HA equ
conc H+ = conc A- (sometimes)
what does the equivalence point on a titration curve show
acid has been neutralised fully by the base (end point)
what is the half equivalence point
point halfway between 0 and equivalence point as pKa = pH at this point
what happens when you add acid to an acidic buffer
the H+ reacts with the high abundance of negative ions provided by the salt to produce more weak acid
what happens when you add a base to an acidic buffer
OH- reacts with H+ so equillibrium shifts to restore lost H+ and pH doesn’t fluctuate much
what can acidic buffers be made from
weak acid and its salt
excess weak acid and strong base
what is a basic buffer
a weak base and its salt
what happens when you add a base to a basic buffer
it reacts with large abundance of positive ions provided by the salt to create more weak base
what happens when you add an acid to a basic buffer
reacts with OH- to create water, equillibrium shifts left to restore lost OH- therefore pH does not go down by a lot
