Question #9caae

1 Answer
Nathan L.
Jun 26, 2017

Kc=5.81×10−3

Explanation:

We're asked to find the equilibrium constant Kc for this reaction, given an initial and final equilibrium concentration.

The equilibrium constant expression for this reaction is

Kc=[SO2]2[O2][SO3]2

If 0.840 moles of SO3 is placed in a 4.50-L container, the initial concentration is

[SO3]=0.840lmol4.50lL=0.187M

We can tabulate now our initial concentrations for each species:

Initial:

  • SO3: 0.187M

  • SO2: 0

  • O2: 0

The changes in concentration, which we'll call the variable x, can be expected via the coefficients of the equation:

Change:

  • SO3: −2x (coefficient of 2)

  • SO2: +2x (coefficient of 2)

  • O2: +x (coefficient of 1)

We know the final equilibrium concentration of O2 is

[O2]=0.130lmol4.50lL=0.0289M

Therefore, the variable x must be equal to this value, because the oxygen concentration change is "+x", and hence 0+x=0.0289

Using this value, we can now find the equilibrium concentrations of all species:

Equilibrium:

  • SO3: 0.187M−2(0.0289M)=0.129M

  • SO2: 0+2(0.0289M)=0.0578M

  • O2: 0+0.0289M=0.0289M

And lastly, we can plug in these values to the equilibrium constant expression to calculate Kc:

Kc=(0.0578M)2(0.0289M)(0.129M)2=5.81×10−3

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