equilibrium

Question 1

a reversible reaction

Answer 1

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

Question 2

what is an example of an equilibrium reaction

Answer 2

production of ammonia
N2 + 3H2 = 2NH3

Question 3

chemical equilibrium

Answer 3

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

Question 4

dynamic state

Answer 4

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

Question 5

dynamic equilibrium

Answer 5

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

Question 6

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

Answer 6

from the balanced equation the ratio is 3:1

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

describe the rate of reaction in the Haber Bosch process

Answer 9

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

Question 10

how do we know when equilibrium has been reached

Answer 10

when the rate of reaction remains constant

Question 11

how would you describe concentration at dynamic equilibrium

Answer 11

all concentrations are constant

Question 12

why does the concentration remain constant when equilibrium is reached

Answer 12

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

Question 13

Le Chatelier’s Principle

Answer 13

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

Question 14

what are the 3 stresses

Answer 14

change in;
pressure
temperature
concentration

Question 15

which side does increasing temp favour

Answer 15

endothermic (+)

Question 16

which side does decreasing temp favour

Answer 16

exothermic (-)

Question 17

what does increasing pressure do to equilibrium

Answer 17

shifts equilibrium to the side with the fewest number of molecules

Question 18

what does increasing concentration do to equilibrium

Answer 18

equilibrium shifts to the other side to relieve stress

Question 19

what does decreasing concentration do to equilibrium

Answer 19

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

Question 20

what effects do catalysts have on equilibrium

Answer 20

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

Question 21

how to answer a conc q

Answer 21

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

Question 22

how do we read an equilibrium equation in terms of temperature

Answer 22

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

Question 23

how to answer a q on temp

Answer 23

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

Question 24

what state does pressure affect

Answer 24

REAGENTS HAVE TO BE GASES

Question 25

what effect does increasing pressure have on equilibrium

Answer 25

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

Question 26

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

Answer 26

no effect as liquid cannot be compressed

Question 27

temp of the formation of ammonia

Answer 27

500 degrees C

Question 28

pressure of the formation of ammonia

Answer 28

200 atm

Question 29

catalyst of of the formation of ammonia

Answer 29

iron

Question 30

why do we not use a lower temperature when forming ammonia

Answer 30

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.

Question 31

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

Answer 31

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

Question 32

is the production of ammonia endo or exo

Answer 32

exo ie more forms at lower temp

Question 33

temperature of the manufacture of sulphuric acid

Answer 33

450 C

Question 34

pressure of the manufacture of sulphuric acid

Answer 34

just above atmospheric pressure

Question 35

catalyst of the manufacture of sulphuric acid

Answer 35

vanadium pentoxide, V2O5

Question 36

what is the contact process

Answer 36

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

Question 37

how is SO2 obtained for the contact process

Answer 37

by burning sulphur in air

Question 38

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

Answer 38

platinum

Question 39

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

Answer 39

it is easily poisoned by impurities in the reaction

Question 40

how is sulphuric acid manufactured from the contact process

Answer 40

SO3 formed in the reaction is dissolved in rainwater to form sulphuric acid SO3 + H2O ---> H2SO4

Question 41

what is the balanced equation for the contact process

Answer 41

2SO2(g) + O2(g) ----> 2SO3(g)

Question 42

what is the equilibrium constant

Answer 42

Kc

Question 43

what is Kc used for

Answer 43

to describe the relationship between the reactants and products

Question 44

what is the only stress that effects Kc

Answer 44

TEMPERATURE

Question 45

how do you write KC

Answer 45

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

Question 46

what do the square brackets represent in the Kc expression

Answer 46

mol/L

Question 47

how does changing temperature affect Kc

Answer 47

if equilibrium shifts to the left the value for Kc decreases if it shifts to the right the value for Kc increases

Question 48

why does pressure not affect Kc

Answer 48

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