Equilibrium

Question 1

what are the 3 principles of dynamic equilibrium?

Answer 1

1) rate of forward reaction = rate of reverse reaction
2) conc of reactants and products doesn’t change
3) occurs in a closed system

Question 2

what is le chatelier’s principle?

Answer 2

when a system in dynamic equilibrium is subjected to a change, the position of the equilibrium will shift to minimise the change

Question 3

what will be the effect of increasing the concentration of a reactant?

Answer 3

eqbm shifts right to minimise the change, so the yield of products increases

Question 4

what will be the effect of removing one of the products from the reaction?

Answer 4

eqbm shifts right to minimise the change, so yield of products increases

Question 5

what will be the effect of increasing pressure on this reaction?
A + B <–> 2C + D

Answer 5

eqbm shifts left- there are less gaseous moles on the left hand side, so yield of A + B increases

Question 6

what will be the effect of decreasing pressure on this reaction?
3H2 + N2 <–> 2NH3

Answer 6

eqbm shifts left- there are more gaseous moles on the left hand side, so yield of hydrogen and nitrogen increases

Question 7

what will be the effect of increasing temperature on this reaction?
A + B<–> C + D
enthalpy change = -150 kJmol-1

Answer 7

eqbm shifts left because the backwards reaction is endothermic

Question 8

which way would eqbm shift if a catalyst was added to a reversible reaction?

Answer 8

catalysts don’t affect eqbm position- the rates of the forward and reverse reactions would increase equally

Question 9

N2 + 3H2 <–> 2NH3
enthalpy change = -92 kJmol-1
what conditions would be needed for a maximised yield, what are the problems with these and what are the compromises?

Answer 9

high pressure- eqbm shifts right because there are less gaseous moles on the right
expensive + dangerous
reduce pressure but still maximise yield of
ammonia
low temp- eqbm shifts right as the forward reaction is exothermic
slow rate of reaction
increase temp high enough to increase rate
without compromising yield

Question 10

what is the Kc constant?

Answer 10

eqbm in terms of concentration- tells us whether eqbm lies more to the left or right

Question 11

write an expression for Kc

Answer 11

Question 12

what does a Kc value of 1 indicate?

Answer 12

eqbm position is halfway between reactants and products- at eqbm

Question 13

what does a Kc value of less than 1 indicate?

Answer 13

eqbm shifted left towards reactants- more reactants than products

Question 14

what does a Kc value of more than 1 indicate?

Answer 14

eqbm shifted right towards products- more products than reactants

Question 15

if a Kc value increases, what does it mean?

Answer 15

that eqbm has shifted more right

Question 16

2SO2 + O2 <–> 2SO3
enthalpy change = -197 kJmol-1
if temperature is increased, what is the effect on position of eqbm, SO3 yield and the value of the Kc constant?

Answer 16

1) eqbm shifts left, as the backwards reaction is endothermic
2) SO3 yield decreases
3) Kc constant decreases