equilibrium Flashcards
a reversible reaction
one in which the products react to give back the reactants
the reaction goes in both directions
what is an example of an equilibrium reaction
production of ammonia
N2 + 3H2 = 2NH3
chemical equilibrium
a state of dynamic balance in reversible reaction where the rate of the forward reaction is the same as the rate of the reverse reaction
ie the concentration remains constant
dynamic state
the reactants are continuously forming products and products are continuously forming reactants
dynamic equilibrium
the rate of the forward reaction is the same as the reverse reaction
why does H2 have a greater concentration than N2 in the Haber Bosch process
from the balanced equation the ratio is 3:1
explain how the concentration of H2 and N2 changes throughout Haber Bosch process
as they react together the concentration of both decreases and the conc of ammonia increases
the conc of H2 and N2 is high at the start as they have not reacted together yet
what is important to remember if drawing the Haber Bosch process graph
at time 0 there is NO ammonia in the reaction vessel. the conc of NH3 must start at (0,0) to show this
describe the rate of reaction in the Haber Bosch process
the rate of the forward reaction decreases and the reverse increases until the rate of the forward is equal to the reverse. this is reflected by the horizontal part of the graph
how do we know when equilibrium has been reached
when the rate of reaction remains constant
how would you describe concentration at dynamic equilibrium
all concentrations are constant
why does the concentration remain constant when equilibrium is reached
even though the reaction is still happening, the rate of the forward and reverse reactions are the same so the relative conc of each substance is not changing
Le Chatelier’s Principle
if a stress is applied to a system at equilibrium the system readjusts to relieve stress applied
what are the 3 stresses
change in;
pressure
temperature
concentration
which side does increasing temp favour
endothermic (+)
which side does decreasing temp favour
exothermic (-)
what does increasing pressure do to equilibrium
shifts equilibrium to the side with the fewest number of molecules
what does increasing concentration do to equilibrium
equilibrium shifts to the other side to relieve stress
what does decreasing concentration do to equilibrium
equilibrium shifts to the side that it was on to reduce stress
what effects do catalysts have on equilibrium
no effect
a catalyst speeds up the rate at which a system reaches equilibrium
they affect both sides of the equation equally so it has no effect on equilibrium position
how to answer a conc q
state which way equilibrium will shift and why:
if more of y is added
equilibrium will shift to the right to relieve stress
more x is produced
if y is removed
equilibrium will shift to the left to relieve stress
yield of x is reduced
how do we read an equilibrium equation in terms of temperature
read from left to right
the arrow pointing towards the delta H shows which reaction relates to the temperature ie if the forward reaction is endo or exo
be careful because they have changed the direction of the arrows before in the exam
how to answer a q on temp
identify which of the reactions is endo or exo
state which way equilibrium will shift and why
increasing temperature will force the equilibrium to shift in the endothermic direction to relieve stress ie to the L/R
thus the yield of x will decrease
decreasing temp will force equilibrium to shift in the exothermic direction to relieve stress ie to the L/R
thus the yield of x will increase
what state does pressure affect
REAGENTS HAVE TO BE GASES
what effect does increasing pressure have on equilibrium
in all GASEOUS reactions it will force equilibrium to shift to the side that decreases volume ie the side with the fewest no of molecules
what effect does pressure have on a reaction happening in an aqueous solution
no effect as liquid cannot be compressed
temp of the formation of ammonia
500 degrees C
pressure of the formation of ammonia
200 atm
catalyst of of the formation of ammonia
iron
why do we not use a lower temperature when forming ammonia
decreasing temperature forces the reaction in the exothermic direction
so more ammonia will be produced
however at lower temperatures the colliding particles have much less kinetic energy so there are fewer effective collisions
this means that the rate of the production of ammonia is very slow at low temp which is actually very expensive thus less profit.
what is a compromise temperature in relation to the manufacturing of ammonia
the temperature is low enough to give an acceptable yield of ammonia but high enough to guarantee an acceptable rate of ammonia formation
is the production of ammonia endo or exo
exo ie more forms at lower temp
temperature of the manufacture of sulphuric acid
450 C
pressure of the manufacture of sulphuric acid
just above atmospheric pressure
catalyst of the manufacture of sulphuric acid
vanadium pentoxide, V2O5
what is the contact process
used to manufacture sulphuric acid
SO2 reacts with oxygen gas over a catalyst
how is SO2 obtained for the contact process
by burning sulphur in air
what is another catalyst that can be used in the contact process
platinum
why is platinum not used as a catalyst in the contact process
it is easily poisoned by impurities in the reaction
how is sulphuric acid manufactured from the contact process
SO3 formed in the reaction is dissolved in rainwater to form sulphuric acid
SO3 + H2O —> H2SO4
what is the balanced equation for the contact process
2SO2(g) + O2(g) —-> 2SO3(g)
what is the equilibrium constant
Kc
what is Kc used for
to describe the relationship between the reactants and products
what is the only stress that effects Kc
TEMPERATURE
how do you write KC
aA + bB –> cC + dD
Kc = top line: [C] to the power of c x [D] to the power of d
bottom line: [A] to the power of a x [B] to the power of b
RIGHT SIDE ALWAYS ON TOP
SQUARE BRACKETS ONLY
what do the square brackets represent in the Kc expression
mol/L
how does changing temperature affect Kc
if equilibrium shifts to the left the value for Kc decreases
if it shifts to the right the value for Kc increases
why does pressure not affect Kc
it changes the no of molecules but the change in volume balances this out in the calculation thus Kc is not affected
