Taylor’s Notes Equilibria and Air
Composition of the Atmosphere
Gas Formula of Gas Percentage Composition
Oxygen O2 21%
Argon Ar 0.9%
Nitrogen N2 78%
Carbon Dioxide CO2 0.04%
Measuring Percentage of Oxygen in Air
Copper is heated and air is passed backwards and forwards over it using gas syringes:
The heated copper reacts with oxygen in the air to form copper oxide
Dynamic Equilibrium Features
Rate of the forwards reaction = rate of the backwards reaction
Concentrations of all reactants and products remains constant
General Changes to the Position of the Dynamic Equilibrium
Change Effect on Position of Equilibrium
Add catalyst It doesn’t change the position
Increase temperature Will shift the position to in the endothermic direction
Increase pressure Will shift the position to the side with the fewest number of gaseous moles
Remove product Shifts the position to the left side (reactants)
Catalysts
A catalyst increases the rate of both the forwards and backwards reaction equally and allows a lower temperature to be used
The equilibrium position remains the same
Measuring Oxygen using Iron
Damp iron is left in a test tube inverted in a beaker of water for a week. The iron will rust consuming all the oxygen in the air.
A ruler can be used to see how the water level has decreased (by the percentage of oxygen present)
Measuring Oxygen using Phosphorus
A piece of white phosphorus (P4) is held in a eudiometer (glass tube with a scale – closed at one end):
Phosphorus is left smouldering in damp air until all oxygen is consumed
As oxygen is consumed, water is pulled up the eudiometer
Change in level gives the percentage of oxygen in the air
Preparation of Oxygen
Oxygen is prepared by the catalytic decomposition of hydrogen peroxide, using a manganese (IV) oxide (MnO2) catalyst
Oxidation Test
If there is oxygen present, it will relight a glowing splint
Oxidation
Many elements react with oxygen to form oxides:
2 Mg(s) + O2(g) → 2 MgO(s) Magnesium – burns with a bright white light to form a white solid (magnesium oxide)
2 H2(g) + O2(g) → 2 H2O(l) Hydrogen – burns with a pale blue flame and a squeaky pop to form water
S(s) + O2(g) → SO2(g) Sulphur – burns with a small blue flame forming sulphur dioxide
Example Question
4NH3(g) + 502(g) ⇌ 4NO(g) + 6H2O(g) ΔH = -907 kJ/mol
The temperature is increase from 100°C to 125°C predict the effect on the yield of Nitric Oxide (NO)
To oppose the temperature increase, the equilibrium shifts to the right as the backwards reaction is endothermic and so the yield of nitric
oxide decreases
The pressure is increased from 30atm to 50atm predict the effect on the yield of Nitric Oxide (NO)
To oppose the pressure increase the equilibrium shifts to the left as the left side has the fewest number of gaseous moles
Composition of the Atmosphere
Gas Formula of Gas Percentage Composition
Oxygen O2 21%
Argon Ar 0.9%
Nitrogen N2 78%
Carbon Dioxide CO2 0.04%
Measuring Percentage of Oxygen in Air
Copper is heated and air is passed backwards and forwards over it using gas syringes:
The heated copper reacts with oxygen in the air to form copper oxide
Dynamic Equilibrium Features
Rate of the forwards reaction = rate of the backwards reaction
Concentrations of all reactants and products remains constant
General Changes to the Position of the Dynamic Equilibrium
Change Effect on Position of Equilibrium
Add catalyst It doesn’t change the position
Increase temperature Will shift the position to in the endothermic direction
Increase pressure Will shift the position to the side with the fewest number of gaseous moles
Remove product Shifts the position to the left side (reactants)
Catalysts
A catalyst increases the rate of both the forwards and backwards reaction equally and allows a lower temperature to be used
The equilibrium position remains the same
Measuring Oxygen using Iron
Damp iron is left in a test tube inverted in a beaker of water for a week. The iron will rust consuming all the oxygen in the air.
A ruler can be used to see how the water level has decreased (by the percentage of oxygen present)
Measuring Oxygen using Phosphorus
A piece of white phosphorus (P4) is held in a eudiometer (glass tube with a scale – closed at one end):
Phosphorus is left smouldering in damp air until all oxygen is consumed
As oxygen is consumed, water is pulled up the eudiometer
Change in level gives the percentage of oxygen in the air
Preparation of Oxygen
Oxygen is prepared by the catalytic decomposition of hydrogen peroxide, using a manganese (IV) oxide (MnO2) catalyst
Oxidation Test
If there is oxygen present, it will relight a glowing splint
Oxidation
Many elements react with oxygen to form oxides:
2 Mg(s) + O2(g) → 2 MgO(s) Magnesium – burns with a bright white light to form a white solid (magnesium oxide)
2 H2(g) + O2(g) → 2 H2O(l) Hydrogen – burns with a pale blue flame and a squeaky pop to form water
S(s) + O2(g) → SO2(g) Sulphur – burns with a small blue flame forming sulphur dioxide
Example Question
4NH3(g) + 502(g) ⇌ 4NO(g) + 6H2O(g) ΔH = -907 kJ/mol
The temperature is increase from 100°C to 125°C predict the effect on the yield of Nitric Oxide (NO)
To oppose the temperature increase, the equilibrium shifts to the right as the backwards reaction is endothermic and so the yield of nitric
oxide decreases
The pressure is increased from 30atm to 50atm predict the effect on the yield of Nitric Oxide (NO)
To oppose the pressure increase the equilibrium shifts to the left as the left side has the fewest number of gaseous moles
