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The importance of investigating conditions that affect rate and yield of chemical reactions

Investigating factors which affect rate and yield is extremely important in industry.  Industries are required to produce high yields of specific products at a reasonable rate and at the lowest cost.  Conditions that produce high yields and / or high rates are often expensive, thus compromises must be made to operate under optimum (best) conditions.

Le Chatelier’s Principle and the Haber process.

The Haber process is used for the manufacture of ammonia.

                                                  Exothermic

N2 (g)3 H2 (g)                                      2 NH3 (g)            ΔH  =  - ve

                                                  Endothermic

 

             4 volumes                                                 2 volumes

 

 

Conditions for the reaction.

 

  1. Temperature of 500ºC :

·       A high temperature increases the rate of attaining equilibrium.

·       The forward reaction is exothermic, therefore a low temperature moves the equilibrium to the right giving a higher yield of ammonia.

·       A medium temperature is used as a compromise.

 

  1. Pressure of 200 atm :

    • A high pressure increases the rate of attaining equilibrium

    •  The forward reaction results in a reduction in volume, therefore a high pressure moves the equilibrium to the right giving a higher yield of ammonia.

 

  1. Catalyst – iron :

·       Considerably increases the rate of attaining equilibrium.

·       The catalyst does not affect the position of equilibrium – yield is not affected.

 

Le Chatelier’s Principle and the Contact process.

The Contact process is used for the manufacture of  sulphuric acid.  This involves the manufacture of sulphur trioxide,SO3

                                                     Exothermic

2SO2 (g)      +         O2 (g)                                            2SO3 (g)          ΔH  =   - ve

                                                      Endothermic

                                    

             3 volumes                                                         2 volumes

 

Conditions for the reaction.

 

1.  Temperature of 450ºC :

·       A high temperature increases the rate of attaining equilibrium.

·       The forward reaction is exothermic, therefore a low temperature moves the equilibrium to the right giving a higher yield of ammonia.

·       A medium temperature is used as a compromise.

 

2.  Pressure of 2 atm :

  • A high pressure would move the equilibrium to the right, but at 450ºC and 2 atm the yield is high – 95%

 

  1. Catalyst – vanadium (V) oxide :

·        Increases the rate of attaining equilibrium.

·       The catalyst does not affect the position of equilibrium – yield is not affected