Chemistry 104 Study Groups

EQUILIBRIUM PROBLEM
ANSWER
 

Exercises

  An equilibrium mixture of SO2, SO3 and O2 gases are maintained in a 2.05 L flask at a temperature at which Kc = 35.5 for the reaction:
2SO2(g) + O2(g) 2SO3
  1. If the numbers of moles of SO2 and SO3 in the flask are equal, how many moles of O2 are present?
  2. If the number of moles of SO3 in the flask is twice the number of moles of SO2, how many moles of O2 are present?

 
 

Answer

  1. 0.0578 mol O2

  2. 0.232 mol O2

 

Explanation

 

This problem requires a bit of thought before using the expression for Kc. Once you realize that [SO2]=[SO3] in part 1, the arithmetic becomes fairly straightforward. Part 2 requires you to realize that 2[SO2]=[SO3], which makes the arithmetic just slightly more complex.

Note that since more product is present in part 2, the reaction moves toward reactants as evidenced by the greater number of moles of O2.

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