![]() These next several examples have a twist. One can never be perfect, so the values for K eq that get published are actually an average of many careful experiments. One more discussion point: you may have noticed the K c answers for #2 and #3 are slightly different when they are supposed to be the same. No, No, No!! Use the concentrations as given. For example, when = 0.0147, the rookie will want to double it, saying "Well, there is a 2HI in the equation. The number two error is wanting to change the concentrations. This is the number one rookie problem in solving these things - forgetting the exponent. The answer is 48.4.Īn important point: remember to square the numerator. I'm not going to write the set-up, but I want you to write it down on your paper. ![]() Yet!!Įxample #3: Using the same equation as above and with the following equilibrium concentrations: You guys don't have that experience, so you don't have the feel. The above problem is routine for me and solely on the basis of experience did I reject my first answer as being wrong (it "felt" wrong). Underscoring my plea for carefulness is the difference between you and me in problem solving. Sure enough, I have made an entry error somewhere in the problem. When I solved this problem while writing the first edition of this tutorial (on December 28, 1998), I first got some really weird looking answer that didn't feel right, so I did it again. Please be very careful in using your calculator to solve these problems. That will NOT make your teacher happy!Įxample #2: The same reaction as above was studied at a slightly different temperature and the following equilibrium concentrations were determined:įrom the data, calculate the equilibrium constant.ġ) Same technique as above, write the equilibrium expression and substitute into it. Please do not march up to him/her and announce they are wrong because some guy on the Internet says so. Some advice: your teacher may insist on putting units on the equilibrium constant. The equilibrium constant does not have any units. For reasons beyond the scope of this lesson, the answer is none. Something of a side issue is what are the units of the K c? And, for that matter, K p. This is what to write:Ģ) Now, all you have to do is substitute numbers into the equilibrium expression:ģ) Solving the above and rounding to the correct number of sig figs (remember those?), we get 60.2 ![]() When the equilibrium concentrations at 25.0 ☌ were found to be:ġ) The first thing to do is write the equilibrium expression for the reaction as written in the problem. The easiest way to explain is by looking at a few examples.īy the way, I'm going to stop using K eq and will start using K c, where 'c' stands for 'concentration.' In the future, you will also study K p, where 'p' stands for 'pressure.'Įxample #1: Calculate the equilibrium constant (K c) for the following reaction: Pp.ChemTeam: Calculate the Equilibrium Constant from Equilibrium ConcentrationsĬalculating the Equilibrium Constant from Equilibrium ConcentrationsĬalculate Equilibrium Concentrations from Initial Concentrations.
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