Learn about Senior Chemistry, Equilibrium 3, in this comprehensive video by bannanaiscool.
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Rob Lederer: Now the other reactions that I showed you had all of the chemicals in the same phase, they were all gases. What happens when you have liquids and solids and gases, maybe even mixed up in a reaction? Well, solids and liquids just made in this reaction anyway, they do not get placed in the equilibrium expression and that's because solids and liquids don't change their concentration. So if a chip off a piece of this piece of matter here and say what the concentration is basically, really what's the density of this piece as opposed to the remaining piece as the same. Solids and liquids don't change their concentration so they don't go in the expression. Did you notice in those last expressions that we wrote and write a K equals the concentration of one product say over the concentration of maybe two others? They K value is a constant. It's always going to be the same number at a given temperature. But you know, we can different concentrations here, here and here as long as the math equals this then that's an equilibrium too and it's fine. So we can have different equilibrium precisions for the chemicals, but they can't still give you and you must give you the same K value. But here is the thing; that means that you can alter the concentrations of chemicals, but you can't alter the concentrations of solids or liquids that inalterable, unalterable, disalterable. So, the point is they don't get put it into the expression and that means this, for this reaction, you would write K equals - well, there is the Co2, so you write concentration of Co2, and then you go - oh, that's a solid, and then over over what? Well that's a solid too. So, it's really just over one and so, the K value actually equals whatever the concentration in the Co2 is, it's that simple and straight forward. Don't include solids don't include liquids unless all the chemicals are liquids. The thing is you can actually change the concentration of liquids because as these two liquids here, which is ethanol and acetic acid and make this ester called ethyl -- and water. The densities are different of these different chemicals, so the volume changes in solution when the volume changes concentration can change. So, I know that's confusing, so here is the only exception. Solids and liquids never put into the expression unless you have all liquids, and then it's a concentration in this times this divided by the concentration of this times this and that equals K. So, what if you have all solids? Well, you just won't. But all liquids look out. You can tell a lot about a reaction just by looking at the K value. So, here are two reactions up here. We have got water forming from its elements and will balance it with one half O2. And let's say at some temperature, I don't know what, but the K value for this is 2.30. Now, here is the formation of ammonia from its elements balanced with the lowest whole number ratio instead the K value here is 2.4 times 10-6+ there is a difference between those two numbers. Now, what is the significance of this K value. Well, 2.30, which tells you this that when you write the expression for this, the equilibrium expression for this reaction, which is here, it's the H2O divided by the concentration of H2 and O2 to the one half power, that just been square root doesn't it? And one half power in the square root. One-third would be something like the cube root of something, right? So, just thought I would throw that in there little bit of math for you. What does the K value of 2.3 tells you. It tells you that the concentration of the products is greater than the reactions at equilibrium because this divided by this gives you a number that's greater than one. If this divided this gives you a number that's greater than one, then this must be higher than this in terms of its numbers. So, what we say is a K value that has a number greater than one means that the products are favored in terms of the amount that is produced at equilibrium. No
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