Lets say that I want to calculate the equilibrium constant $K$ for a chemical reaction where $\ce{A -> B}$

$$K = [\ce{A}]/[\ce{B}]$$

where $[\ce{A}]$ is the concentration of $\ce{A}$ and $[\ce{B}]$ is the concentration of $\ce{B}$ at equilibrium

I have measured the quantities $[\ce{A}]$ and $[\ce{B}]$ and thus have two sets of data.

To calculate $K$ should I:

  • Take the ratio of $[\ce{A}]$ and $[\ce{B}]$ at each data point and then calculate a mean average of all of the $K$ values?

  • OR Plot a graph of $[\ce{A}]$ against $[\ce{B}]$ and use the gradient of the best fit line as the value of $K$?

My instinct tells me it is the former as the straight line plot on excel has a non-zero intercept (which is not reasonable). If it is the first option, can you explain to me why it is so?

  • $\begingroup$ How do you know you're at equilibrium? We need a better description of your experiment to answer your question. Why are there different concentrations of [A] and [B]? What did you vary to get these different concentrations? $\endgroup$ – Curt F. Feb 28 '18 at 3:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.