2 SO 3 (g) ? 2 SO 2 (g) + O 2 (g) K C = 0.21 What are the equilibrium concentrat
ID: 706365 • Letter: 2
Question
2 SO3(g) ? 2 SO2(g) + O2(g) KC = 0.21
What are the equilibrium concentrations when [SO3]i = 0.157M?
Start by constructing a RICE chart for this reaction and setting up your KC equation. You may NOT use the quadratic equation or any sort of solver or any similar crutch. Do this by hand with a simple calculator. We may have discussed that it is possible to use an iterative process to solve for equilibrium concentrations without having to use the quadratic equation, and so that is what you will do for this.
Make an assumption for the change for SO3 (start with x = 0)
Solve for the other x, which is the change for the other two species.
Each iteration you should see the values get closer and closer together. Once both values for x are the same (once they are within 0.1% difference or so), you must be done!
Don’t forget to now use your value for x to report the equilibrium concentrations and also to verify that those concentrations plug in to get the value of KC that you were given:
[SO3]eq
[SO2]eq
[O2]eq
KC
[SO3]eq
[SO2]eq
[O2]eq
KC
Explanation / Answer
2 SO3(g) <-------->2 SO2(g) + O2(g) KC = 0.21
Kc= [SO2]2 [O2]/[SO3]2=0.21
[SO3]i = 0.157M
Preparing the ICE table
Component Initial concentration change Equilibrium concentration
SO3 0.157 -2x 0.157-2x
O2 0 x x
SO2 0 2x 2x
KC= (2x)2* x/ (0.157-2x)2= 0.21
4x3/ (0.157-2x)2=0.21, when solved using excel, x= 0.05236
[SO3]=0.157-2*0.05236= 0.05238M, [SO2]= 2*0.05236= 0.105M and [O2]=0.05236M
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