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9.5 Industrial Chemistry: 2. Equilibrium reactions in industrial processes

Syllabus reference (October 2002 version)

Answers to questions:

1. 1. 
      
      
      
2. You need to find the concentrations, at equilibrium, of HI, I₂ and H₂.

   If you start with 5 mol of HI in a 1 L container, then its initial concentration is 5 molL^-1.

   You start with 5 mol HI and end up with 1 mol HI, so 4 mol HI has changed to H₂ and I₂.

   Looking at the mole ratio in the equation, we can see that:

   1 mol HI would produce 0.5 mol H₂ and 0.5 mol I₂.

   So 4 mol HI would produce 2.0 mol H₂ and 2.0 mol I₂.

   It helps to draw up a reaction table, sometimes called an ICE (initial, change, equilibrium) table as shown below.

   Equation	H2(g)    +     I2(g)      2HI(g)
   Initial concentration	0                    0	5
   Change in concentration	+2.0              +2.0	-4
   Equilibrium concentration          molL-1	2.0                2.0	1

   Now we can calculate K

   

   Note: K value is different from K calculated in question1b) because the temperature is different.

3. 
   
   1. Graph A shows changes in the concentration of hydrogen - starting at 2 molL^­1.
      
      Graph B shows changes in the concentration of HI - starting at 0 molL^­1.
      
      
   2. at 12 minutes
      
      
   3. 
      

      Equation	H2(g)     +     I2(g)      2HI(g)
      Initial concentration	2                       3	0
      Change in concentration	-0.5                  -0.5	+1.0
      Equilibrium concentration              molL-1	1.5                   2.5	1

      
      

Note: Temperature would have been similar to that in question 2 as the K values are similar

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