Reactors and equilibria

Question 1

Batch reactors

Answer 1

-No material enters or leaves reactor
-Perfect mixing
-Rate of accumulation of A in reactor = -rate of loss of A in reaction

Question 2

Plug flow reactors

Answer 2

-Input of A, moles/time = FA -Output of A = FA + dFA
-Input conversion of A = XA -Output conversion of A = XA + dXA
-Disappearance of A by reaction, moles/time = (-rA)dVr

Question 3

What is the expansion coefficient and when is it used?

Answer 3

• ε = (final - initial moles)/ initial moles
  -Used when there is a change in the number of moles/volume

Question 4

Continuous stirred tank reactor

Answer 4

-Perfect mixing occurs, assumed
-Concentration is the same throughout and equal to conc. out

Question 5

If Kc/Kp is&raquo_space; 1 what does that show?

Answer 5

-Reaction is product favoured
-Product dominates at equilibrium

Question 6

If Kc/Kp is &laquo_space;1 what does that show?

Answer 6

-Reaction is reactant favoured
-Reactant dominates at equilibrium

Question 7

What is a reaction quotient?

Answer 7

-Shows if a reaction is at, before or after equilibrium
-Uses the same equation as equilibrium constant, but uses current concentrations

Question 8

What does it mean if Q < Keq

Answer 8

-Forward reaction is spontaneous
-Not yet at equilibrium

Question 9

What does it mean if Q > Keq

Answer 9

-Reverse reaction is spontaneous
-Past equilibrium and will now work backwards

Question 10

What does it mean if Q = Keq

Answer 10

Reactants and products are at equilibrium

Question 11

What does heterogeneous equilibria mean for the equilibrium constant?

Answer 11

If a solid or liquid is present, the concentration of it is constant and can be included in the value of Keq itself leaving just the gas conc. on the right side of the equation
e.g CaCO3 (s) <-> CaO(s) + CO2 (g)
Keq = [CO2]

Question 12

How is conc. changed by Le Chateliers principle

Answer 12

-Greater conc. than equilibrium, some of substance is consumed
-Less conc. than equilibrium, react to produce more of substance

Question 13

How is pressure changed by Le Chateliers principle

Answer 13

-Lower pressure -> shift to side with more moles
-Too high pressure -> shift to side with fewer moles

Question 14

How is temp. changed by Le Chateliers principle

Answer 14

-Shifts to create or remove the heat to balance the temp, shift changes depending on endo or exothermic

Question 15

How do catalysts effect the equilibrium position

Answer 15

-They don’t
-Can’t change point of equilibrium, just the speed it is reached

Question 16

What is chemical potential?

Answer 16

-Equal to the Gibbs free energy for 1 mole
µ = G = H - TS
-At equilibrium as the same value for a given component in each phase

Question 17

What is G when two or more chemical species are in equilibrium?

Answer 17

G = 0

Bc the temp and pressure of all the components must be identical at equilibrium