Determining final concentrations of a Reaction given an equilibrium K

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Discussion Overview

The discussion revolves around determining the final concentrations of reactants and products in a chemical equilibrium reaction involving sulfur dioxide and oxygen converting to sulfur trioxide. Participants explore the setup of the equilibrium expression and the application of the RICE table method, focusing on the implications of the equilibrium constant (Kc) and the initial concentration provided.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents the equilibrium reaction and the initial concentration of SO3, seeking to find the final concentrations of SO2, O2, and SO3 using Kc = 0.15.
  • Another participant suggests that reversing the reaction is unnecessary and questions the expected outcome of the calculations.
  • A different participant proposes that the issue may stem from rounding errors in the variable "x," which affects the back-calculation of concentrations.
  • The original poster later confirms that their cubic equation was correct, indicating a potential error in the provided answer sheet rather than in their calculations.

Areas of Agreement / Disagreement

Participants generally agree on the validity of the original poster's setup and calculations, but there is some uncertainty regarding the necessity of reversing the reaction and the implications of rounding errors. The discussion does not reach a consensus on the expected answer due to the mention of an error in the answer sheet.

Contextual Notes

Participants express concerns about the accuracy of the calculations, particularly regarding the treatment of the variable "x" and its impact on the equilibrium expression. There is also a mention of the potential for significant error due to rounding in the context of a nearly complete conversion.

Who May Find This Useful

This discussion may be useful for students studying chemical equilibrium, particularly those working on problems involving the application of equilibrium constants and RICE tables in reaction scenarios.

BrettJimison
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Homework Statement



Rxn: 2SO2 (g) + O2 (g) \Leftrightarrow 2SO3 (g)

If the initial concentration of SO3 is .500 M (moles/liter) @1500K, what are the final concentrations of [SO2], [O2] and [SO3]. Kc = .15

Stop when you get to the cubic equation

Homework Equations



RICE table

Kc= [SO3]2/ [O2][SO2]2 This is equilibrium quotient for forward reaction. I will flip it to get reverse reaction Kc equation



The Attempt at a Solution



This is the Kc given for the forward reaction. If I flip the reaction around I invert the Kc and it becomes = 6.6667 (for the reverse reaction)

I then used a "rice" table with the initial concentration of SO3 and "x" variable for the SO2 and O2[

Plugging these values in I get the kc equation:

6.6667= [2x]2[x]/[.500-2x]

I'm not getting the correct cubic equation when expanding this quotient. I'm sure of my math, so I was wondering if I'm setting up the quotient wrong? - Thanks!
 
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You don't need to reverse the reaction (you flipped and calculated the inverse of the Kc, which effectively cancels out).

What is the "correct" answer you are expecting to get? At first sight I don't see anything wrong with your work.
 
Looks OK to me too. Maybe the problem is this is a fairly complete conversion so don't round down too much your x as this could introduce considerable error in your (0.5 - 2x) when you back calculate to check?

(I get x = 0.24566)
 
Thanks for the input Borek and epenguin.
If turns out there was an error on the answer sheet I was given.
My cubic equation was correct after all.
 

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