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LC Chemistry > equilibrium > Flashcards

equilibrium Flashcards

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1
Q

a reversible reaction

A

one in which the products react to give back the reactants
the reaction goes in both directions

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2
Q

what is an example of an equilibrium reaction

A

production of ammonia
N2 + 3H2 = 2NH3

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3
Q

chemical equilibrium

A

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

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4
Q

dynamic state

A

the reactants are continuously forming products and products are continuously forming reactants

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5
Q

dynamic equilibrium

A

the rate of the forward reaction is the same as the reverse reaction

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6
Q

why does H2 have a greater concentration than N2 in the Haber Bosch process

A

from the balanced equation the ratio is 3:1

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7
Q

explain how the concentration of H2 and N2 changes throughout Haber Bosch process

A

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

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8
Q

what is important to remember if drawing the Haber Bosch process graph

A

at time 0 there is NO ammonia in the reaction vessel. the conc of NH3 must start at (0,0) to show this

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9
Q

describe the rate of reaction in the Haber Bosch process

A

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

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10
Q

how do we know when equilibrium has been reached

A

when the rate of reaction remains constant

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11
Q

how would you describe concentration at dynamic equilibrium

A

all concentrations are constant

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12
Q

why does the concentration remain constant when equilibrium is reached

A

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

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13
Q

Le Chatelier’s Principle

A

if a stress is applied to a system at equilibrium the system readjusts to relieve stress applied

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14
Q

what are the 3 stresses

A

change in;
pressure
temperature
concentration

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15
Q

which side does increasing temp favour

A

endothermic (+)

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16
Q

which side does decreasing temp favour

A

exothermic (-)

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17
Q

what does increasing pressure do to equilibrium

A

shifts equilibrium to the side with the fewest number of molecules

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18
Q

what does increasing concentration do to equilibrium

A

equilibrium shifts to the other side to relieve stress

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19
Q

what does decreasing concentration do to equilibrium

A

equilibrium shifts to the side that it was on to reduce stress

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20
Q

what effects do catalysts have on equilibrium

A

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

21
Q

how to answer a conc q

A

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

22
Q

how do we read an equilibrium equation in terms of temperature

A

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

23
Q

how to answer a q on temp

A

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

24
Q

what state does pressure affect

A

REAGENTS HAVE TO BE GASES

25
Q

what effect does increasing pressure have on equilibrium

A

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

26
Q

what effect does pressure have on a reaction happening in an aqueous solution

A

no effect as liquid cannot be compressed

27
Q

temp of the formation of ammonia

A

500 degrees C

28
Q

pressure of the formation of ammonia

A

200 atm

29
Q

catalyst of of the formation of ammonia

A

iron

30
Q

why do we not use a lower temperature when forming ammonia

A

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.

31
Q

what is a compromise temperature in relation to the manufacturing of ammonia

A

the temperature is low enough to give an acceptable yield of ammonia but high enough to guarantee an acceptable rate of ammonia formation

32
Q

is the production of ammonia endo or exo

A

exo ie more forms at lower temp

33
Q

temperature of the manufacture of sulphuric acid

A

450 C

34
Q

pressure of the manufacture of sulphuric acid

A

just above atmospheric pressure

35
Q

catalyst of the manufacture of sulphuric acid

A

vanadium pentoxide, V2O5

36
Q

what is the contact process

A

used to manufacture sulphuric acid
SO2 reacts with oxygen gas over a catalyst

37
Q

how is SO2 obtained for the contact process

A

by burning sulphur in air

38
Q

what is another catalyst that can be used in the contact process

A

platinum

39
Q

why is platinum not used as a catalyst in the contact process

A

it is easily poisoned by impurities in the reaction

40
Q

how is sulphuric acid manufactured from the contact process

A

SO3 formed in the reaction is dissolved in rainwater to form sulphuric acid

SO3 + H2O —> H2SO4

41
Q

what is the balanced equation for the contact process

A

2SO2(g) + O2(g) —-> 2SO3(g)

42
Q

what is the equilibrium constant

A

Kc

43
Q

what is Kc used for

A

to describe the relationship between the reactants and products

44
Q

what is the only stress that effects Kc

A

TEMPERATURE

45
Q

how do you write KC

A

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

46
Q

what do the square brackets represent in the Kc expression

A

mol/L

47
Q

how does changing temperature affect Kc

A

if equilibrium shifts to the left the value for Kc decreases

if it shifts to the right the value for Kc increases

48
Q

why does pressure not affect Kc

A

it changes the no of molecules but the change in volume balances this out in the calculation thus Kc is not affected

LC Chemistry (22 decks)

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