Chemical Equillibria Part 1

Question 1

Define dynamic equillibrium.

Answer 1

Rate of forward and reverse reactions are equal
Concentration of the reactant and the products remain constant

Question 2

Define Le Chatelier’s Principle.

Answer 2

Equilibrium shifts towards the forward or reverse reaction as of consequence in change of concentration, pressure or temperature.

Question 3

Define the equilibrium constant (Kc)

Answer 3

Kc = Concentration of products / Concentration of reactants

Kc is unaffected by pressure and catalysts
No solids or pure liquids are included in the expression BUT are included in the table when calculating Kc value

Kc Tables:
Always label columns and rows the same way
If a substance is not mentioned, give it zero
Use ratios of the big numbers to complete middle row
Then complete each column

Question 4

Define Kp.

Answer 4

Equilibrium constant in terms of pressure.

Kp = p(reactants) / p(products)

Question 5

What are the rules of Kc and Kp?

Answer 5

Only a change in temperature will cause Kc and Kp to change
If forward reaction is favoured, then Kc and Kp increase
If reverse reaction is favoured, then Kc and Kp decrease

Question 6

Describe Chemical Equilibrium in industry.

Answer 6

Nitrogen: Unreactive due to triple bond
Diatomic
Non-polar
Used in the production of ammonia

Ammonia: Used in fertilisers
Overuses of fertilisers is known as Eutrophication:
- Causes algae to grow
- Algae blocks sunlight
- Plants decompose
- Bacteria increases
- Bacteria produce more CO2 and less O2
- Fish die

Question 7

Describe the Haber Process.

Answer 7

Process used to manufacture ammonia (NH3)
Ammonia is used for fertilisers
Conditions:
200 atm
400-450 degrees C
Fe catalyst

N2(g) + 3H2(g) <-> 2NH3(g)

Question 8

Describe the Contact Process.

Answer 8

Production of H2SO4
Steps:
1. Roasting of sulfur in air:
S + O2 -> SO2
Uses - Food preservatives, bleaching of wood fibres to make paper

2. Formation of sulfur trioxide:
   2SO2 + O2 <-> 2SO3 Delta H = negative
   Conditions for maximum yield:
   450 degrees C: Temperature is low enough that forward, exothermic reaction is favoured
   1-2atm: Pressure is high enough that forward reaction (fewer gas molecules) is favoured. Not too high as it is expensive to maintain
   Vanadium Pentoxide (V2O5) catalyst
3. Formation of Oleum:
   H2SO4 + SO3 -> H2S2O7
   Water cannot be reacted directly with sulfur trioxide as it is too volatile and a toxic gas is produced
4. Formation of Sulfuric Acid:
   Oleum is reacted with water
   H2S2O7 + H2O -> H2SO4
   Uses - car batteries, manufacturing of paint

Question 9

What is the environmental impact of the Contact Process?

Answer 9

Causes acid rain which causes deterioration of:
Lakes
Destroys crops and vegetation
Damages buildings: SO2 + H2O -> H2SO4 (acid rain)

Question 10

How are Nitrogen Oxides formed?

Answer 10

During lighting
Inside car engines
N2 + 2O2 -> NO2

Question 11

How are Nitrogen Oxides removed from exhaust fumes?

Answer 11

By catalytic converter.
2NO + 2CO -Platinum catalyst-> N2 + 2CO2 (Heterogenous catalyst)

Question 12

What are the negative impacts of Nitrogen Oxides?

Answer 12

Catalyses the formation of SO3:
SO2 + NO2 -> SO3 + NO
2NO + O2 -> 2NO2
Nitrogen Oxides contribute to:
Photochemical smog
Formation of ozone
PAN (peroxyacetyl nitrate)
All of which are dangerous to health