I'm having a hard time figuring out when to use the Kc equation to solve for a concentration of a reactant/product versus when to use an ice table and the quadratic formula. For questions that give you the molar concentrations of all except one reactant/product and ask you to find the equilibrium concentration of that unknown reactant/product, which method would you use?
For example, question 5I.1 in the textbook.
When to use Kc equation vs. When to use ice table
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Re: When to use Kc equation vs. When to use ice table
This might not completely answer your question, but only use the ICE tables when the question states the reaction involves a weak acid or base. We use the quadratic formula after using the ICE table and we get something like Kc= (x^2)/(# - x) and Kc is something like __ x 10^-y and y is less than 3. This means that the x in the denominator is not negligible and we cannot approximate that Kc= (x^2)/(# ).
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Re: When to use Kc equation vs. When to use ice table
If you are given the molar concentration for all except one reactant/product and are asked to find the equilibrium concentration of that unknown reactant/product you would only be able to use the Kc equation to solve for a concentration if you are told that the quantities you were given are all at equilibrium. However if the quantities you are given are the initial values (not at equilibrium) then you have to use an ICE table to solve for the equilibrium values.
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Re: When to use Kc equation vs. When to use ice table
The ICE table is useful when there is a change in the concentrations since it helps visualize that change, it is most useful in problems that just have a change in concentrations in general. A thing to keep in mind, is that if you are given a change in concentration problem and also a Kc value, it is your hint that you might need to use the K equation along with the ICE table.
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Re: When to use Kc equation vs. When to use ice table
Follow-up question: do we need to know how to convert from K to Kc?
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