7. Equilibrium

Question 1

Whta is dynamic equilibrium

Answer 1

Dynamic equilibrium: equilibrium at which forward and reverse reactions are happening

Rate of forward and reverse reaction are the same

Question 2

What are the feautures of equilibrium state?

Answer 2

Concentrations are constant but reaction rates are the same

(conc not the same because of unproportional equilibrium constants)

Question 3

What are the limitations of Kc?

Answer 3

It can only be calculated for homogenous equilibrium (reactants and products of same state) Kc=[a]a[B]b/[C]c[D]d

For heterogenous equilibrium - Kc calculate from deltaG = -RTlnK

Question 4

How is equilibrium constant Kc calculated form experimental data?

Answer 4

Kc changes with temperature

Question 5

For what is the reaction quotient Q used?

Answer 5

Allows to identified which reaction forward or reverse is favoured not at equilibrium

Question 6

How does invertingin teh reaction, changing conc and adding reactions changes Kc?

Answer 6

Manipulations can be done:

Question 7

State Le Chatelier’s principle

Answer 7

Le Chatelier’s principle: when a system at equilibrium is disturbed, it will respond to minimise the effect of the change (will respond in the opposite way)

Question 8

How does a catalyst affect both the forward and the reverse reaction?

Answer 8

No effect on Kc - just equilibrium reached faster

Question 9

What are the factors which can affect the position of reaction and Kc?

Answer 9

Question 10

What are the industrial reactions which are based on equilibrium?

Answer 10

• Haber process
• Contact process
• Production of methanol

Question 11

Explain Haber process

Answer 11

N₂ + 3 H₂ -> 3 deltaH = - 93 kJ mol

Optimum conditions:

• NH3 removed as it forms - increases yield
• high pressure 2X10⁷
• moderate temp 450C (exoth)
• catalyst: powdered iron, ruthenium (catalyst increases the rate of both forward and reverse reactions)

Question 12

Explain Contact process

Answer 12

2 SO₂ + O₂ -> 3 deltaH = -196kJ mol

Optimum conditions:

Question 13

Explain production of methanol

Answer 13

CO + 2 H₂ -> 3OH deltaH = -90 kJ mol

Ideal conditions:

Question 14

What value of Gibbs free E says about the reaction?

Answer 14

Question 15

What is the free E change when equilibrium is being established? (forward reaction spontaneous)

Answer 15

Question 16

What values are of G and S at equilibrium?

Answer 16

S - maximum (most entropy - most disorder)

G - minimum (lowest point at equilibrium)

Question 17

What is the relationship between Kc and deltaG?

Answer 17

deltaG = -RT lnK

R - gas constant

T - temperature

lnK - natural log of Kc

Question 18

How to calculate Q and Kc from a graph?

Answer 18

Until reaction rates are constant - no equilibrium - Q is calculated

When reaction rates are constant - equilibrium - Kc calculated

When Q approaches Kc from higher to lower (Q>Kc) - reaction procedes to the left

When Q approaches Kc from lower to higher (Kc>Q) - reactions proceeds to the right

When Q=Kc - equilibrium