Reversible Reactions and Dynamic Equilibrium

• Sign for reversible reactions

  
• Hydrogen is obtained from natural gas
• The Haber process produces ammonia from nitrogen and hydrogen.
• The equation for this reaction is N2 + 3H2 → 2NH3
• In a reactor, nitrogen and hydrogen at a high pressure are heated and passed over a catalyst.
• The temperature in reactor is 450*c
• The catalyst used in the reactor to produce ammonia is iron
• How does a catalyst speed up a reaction?

  lowers activation energy.
• A mixture of gases leaves the reactor. The mixture contains ammonia, nitrogen and hydrogen. Describe what happens to this mixture of gases in the condenser.


  Gases are cooled

  ammonia condenses

  nitrogen and hydrogen are recycled
• Ammonia solution is alkaline.
• Ammonia solution is used in cleaning products to remove grease from kitchen surfaces.
• Where does the nitrogen used in the Haber process come from?

  Air
• explain why high temperatures make reactions faster

  particles move faster

  particles collide more often
• The condenser separates the ammonia from the unreacted nitrogen and hydrogen by turning the ammonia into a liquid
• What name is given to reactions that heat the surroundings?

  Exothermic
• In the reactor only a small amount of the nitrogen and hydrogen is changed into ammonia. Why?

  The reaction is reversible
• What happens to the unreacted nitrogen and hydrogen from the reactor?

  Recycled
• Factories that make ammonia are very large and operate night and day
• The Haber process has helped to increase food production. Explain why.


  used to make fertilisers
• Ammonia factories are often near towns. Suggest why.

  good transport links
• Explain why the best yield of ammonia at equilibrium is obtained: at low temperature


  Reaction is exothermic
• Explain why the best yield of ammonia at equilibrium is obtained: at high pressure.

  More reactant molecules than product molecules
• The yield of ammonia is only about 15%.

  Why can the yield not be 100%?

  the reaction is reversible
• In a chemical compound, two or more elements or different atoms are bonded
• The chemical formula of ammonia is NH3. This shows that there is one atom of nitrogen and three atoms of hydrogen in each molecule of ammonia. These atoms are joined by bonds that are formed by sharing pairs of electrons. This type of bond is called a covalent bond.
• The Haber Process is usually carried out at a higher temperature than that which would produce the maximum yield. Suggest why.

  higher rate of reaction

  good rate of production
• Ammonia can be converted to ammonium nitrate by adding an acid. Name this acid


  Nitric Acid
• process to make ammonia

  
• Explain why changing the pressure does not affect the yield of hydrogen at equilibrium.

  Same number of molecules on both sides
• Suggest why the best yield of hydrogen at equilibrium is obtained at low temperatures.

  Forwards reaction is exothermic
• The temperature used in industry needs to be high enough for the reaction to take place quickly

   
• Explain, in terms of particles, why the rate of reaction increases when the temperature is increased.

  Particles gain energy and move faster so there are more collisions
• The Haber process uses a temperature of 450 °C and a pressure of 200 atmospheres
• The Haber process uses a temperature of 450 °C and a pressure of 200 atmospheres

  Explain why

  at low temperatures the reaction is too slow

  450 °C gives a reasonable yield at a fast rate

  200 atm. gives a reasonable yield at a reasonable cost
• when the reaction reaches equilibrium

  the mass of each substance does not change

  the rates of the forward reaction and reverse reaction are equal
• The rate of reaction between gases is affected by changing the pressure
• When the pressure of the reacting gases is increased, the rate of reaction increases.

  This is because at higher pressures the distance between the particles decreases.

  This means that the frequency of collisions increases.
• way of changing the rate of reaction between gases.

  Pressure

  Change in temperature

  Catalyst
• Explain why a change in pressure does not affect the colour of an equilibrium mixture

  No change in equilibrium position as no gas present
• A pressure of 285 atmospheres is not used in the Haber process instead of 200 atmospheres. Give one reason why.

  Energy costs would be higher