Achieve hw 1, #2

[Tianna Nguyen 1I]

Hi, I'm struggling to get the correct answer for this question:
"At a certain temperature, 0.900 mol SO3 is placed in a 2.00 L container.
2SO3(g)↽−−⇀2SO2(g)+O2(g)
At equilibrium, 0.120 mol O2 is present. Calculate Kc."
My equation for Kc came out to be (0.12^2)(0.06)/(4.38^2) but I'm not sure where I went wrong.

[Anne Mariano 3F]

You got the first half of your equation correct, the (0.12^2)(0.06) part.

For the denominator, it will be found by:
1. Find the final amount of 2SO3. It would look like 0.900 - 2(0.120)
2. Find molar concentration. 0.66mol/2L = 0.33M
3. Plug in the answer in the denominator, remember to square it.

[Adithi Ayyala 2G]

Hey Tianna! Essentially, due to the fact that we were given the concentration of O2 at equilibrium, this problem is asking us to use stoichiometry to find our concentration of SO3. Our final equation would resemble "Kc= ([2SO2]^2) [O2]/ ([2SO3]^2), in which we would plug in our values from the ice chart, and find our final SO3 concentration.

[Tyler_Kim_2G]

My problem was slightly different, but it seems like you got the correct equilibrium concentrations for the products. However, the equilibrium concentration for SO3 seems to be very large. The initial molarity here should be 0.45 M (this was given), and there should be a change of -2x. Because you got the correct equilibrium concentrations for the products, I believe you should be able to solve from there.

[Jonathan Garcia 2D]

It looks like you had an issue with your denominator for your Kc. To get molar concentration you need to do mol x L^-1. For 2SO3 this would be .66mol/2L =.33M

Your answer would come out to be (0.12^2)(0.06)/(.33^2).