quilibria
reversible reactions reactions can go forward and backward symbol
wardsreactioninnamiceauerBrium
fief's 111 1 It
closedsystem Forward reaction initially reactants are used upquickl
p
Backward reaction initially reactants are reformed
owly but then speedup as the conc of products increases
Lech atelier's principle states that if a reaction at equilibrium issubjectedto
change in pressure temperatureorcocentrationpositionof I will move to
interact the change se shifts to left make more reactants
I shifts to right make more products
only works in homogenousequilibria where reactants and products in the
9Mhingidnitgitone
if you increase conc I will shift to try to reduce the conc
A conc of reactant will shift E to the right to use it up and t conc so mor
199h'atngrifgufeedmp
if yugursincrearsteemie will shift to try reducetemp
if SH is ve then forward reaction is exothermic or temp will shift E in
he endothermicdirectionso more reactants produced vice versa for u temp
changing pressure if you increase pressure I will shift to try reduce
res sure
r pressure will shift I to side with fewest number of gas
articles e g l 3h c g i t Na lg T2 NH3 g I will shift to the right
o more NH3 product produced vice versa fort pressure
catalyst no effect on the positionof as a catalyst will speedup the
ate of forward and backward reaction equally catalyst speeds up the
ate at which equilibrium is reached but have no effect on yield
making ethanol callacg H2O g I CansoHcg AH ask Jm ol
conditions Pressure Goatmospheres
Temp 3000C
catalyst isphosphoric acid HzPoa
forward reaction exothermicso decreasing temp will shift E to
he right producing more ethanol However a lower temp lower rate 7300
a compromise between yield and rate
Highpressure means shifts rightproducing more ethanol and high
res sure increases rate too However high pressureenvironments are
expensive
to thicker more robust vessels and pipesneeded there is a compromise
e tween yield speed and cost
Kc Equilibrium constant
worked out from molar conc in reaction
e 912 At B Eze D Skc expression C 2 D products
molevalveinfrontofeachspeciesarepowers A 2 B
inthe Kcexpression
reactants
calculation involves substitution of conc values given into Kc expression
units write units top and bottom and cancel simplify invert powers if
more units on the bottom Donothing if on top
conc of a species can be worked out before working out Kc if mass and
Olume use mass and Mr to find moles use known moles to calculate
nitial moles change moles Equilibrium moles ICE
if I L ratio we can assume conc are the same when findingunknown
one at E using Kc value
What affects value of KC
Temp Kc is only valid for one temp changing temp will change
conc hence ke will change too if temp change causes to shift right
c will t vice versa for shift to left
ke not affected by changes in confituretire's're'nate ofcatalystIs
reversible reactions reactions can go forward and backward symbol
wardsreactioninnamiceauerBrium
fief's 111 1 It
closedsystem Forward reaction initially reactants are used upquickl
p
Backward reaction initially reactants are reformed
owly but then speedup as the conc of products increases
Lech atelier's principle states that if a reaction at equilibrium issubjectedto
change in pressure temperatureorcocentrationpositionof I will move to
interact the change se shifts to left make more reactants
I shifts to right make more products
only works in homogenousequilibria where reactants and products in the
9Mhingidnitgitone
if you increase conc I will shift to try to reduce the conc
A conc of reactant will shift E to the right to use it up and t conc so mor
199h'atngrifgufeedmp
if yugursincrearsteemie will shift to try reducetemp
if SH is ve then forward reaction is exothermic or temp will shift E in
he endothermicdirectionso more reactants produced vice versa for u temp
changing pressure if you increase pressure I will shift to try reduce
res sure
r pressure will shift I to side with fewest number of gas
articles e g l 3h c g i t Na lg T2 NH3 g I will shift to the right
o more NH3 product produced vice versa fort pressure
catalyst no effect on the positionof as a catalyst will speedup the
ate of forward and backward reaction equally catalyst speeds up the
ate at which equilibrium is reached but have no effect on yield
making ethanol callacg H2O g I CansoHcg AH ask Jm ol
conditions Pressure Goatmospheres
Temp 3000C
catalyst isphosphoric acid HzPoa
forward reaction exothermicso decreasing temp will shift E to
he right producing more ethanol However a lower temp lower rate 7300
a compromise between yield and rate
Highpressure means shifts rightproducing more ethanol and high
res sure increases rate too However high pressureenvironments are
expensive
to thicker more robust vessels and pipesneeded there is a compromise
e tween yield speed and cost
Kc Equilibrium constant
worked out from molar conc in reaction
e 912 At B Eze D Skc expression C 2 D products
molevalveinfrontofeachspeciesarepowers A 2 B
inthe Kcexpression
reactants
calculation involves substitution of conc values given into Kc expression
units write units top and bottom and cancel simplify invert powers if
more units on the bottom Donothing if on top
conc of a species can be worked out before working out Kc if mass and
Olume use mass and Mr to find moles use known moles to calculate
nitial moles change moles Equilibrium moles ICE
if I L ratio we can assume conc are the same when findingunknown
one at E using Kc value
What affects value of KC
Temp Kc is only valid for one temp changing temp will change
conc hence ke will change too if temp change causes to shift right
c will t vice versa for shift to left
ke not affected by changes in confituretire's're'nate ofcatalystIs
