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Calculate the rate constant, Kc, for the reaction below

Jules Bruno
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So here this one's a lot more complicated. What we're gonna say here is we need to find the K value Casey value for this equation here. We're gonna call this K C four. This will be K C 12 and three. Since we're gonna need some room to do this, guys, I'm gonna take myself out of the image so we have more room to work with. What? So our best strategies for a question like this is, since we're trying to isolate that equation above, we have to look and see. Where do we see each one of these elements? So what we need to do first is find h gas and we're gonna notice that we see h gas right here. Now we have to manipulate this one in red, so it matches up with this one in blue. So what to changes? Do I need to do to it first? The H in red is a product, but we needed to be reacted. So we need to reverse the reaction once we reverse it. We also need to realize that there's a two in front of this H But over here in the blue box there, Isn't it a two. So we need to divide by two. And we just said dividing by two is the same thing as multiplying by half. So we have to reverse it and multiply by a half. Remember, dividing by two is the same thing is multiplying by half. So now our equation becomes H gas gives me half H two gas. When we reverse it, Que becomes 1/11 0. and because we multiplied by a half, half becomes the power. And just remember, half power really means square root. Okay, we're going to say that this right here got manipulated so we no longer care about it. And remember, we did all of this so that the red H gas that we have matches up with the H gas in the blue box. We're basically trying to manipulate these three equations so that they look like the compounds in the blue boxes above next we're gonna see where do we see br br gas here in the blue box? It's a reactant, but over here it's a product also here in the blue box, it doesn't have a coefficient in front of it. But here it has a two So the two changes are the same We need to reverse it So it becomes a reacted to and we need to divide by two which is the same thing as multiplying by a half. So this becomes BR gas gives me half br to gas So we reversed it So it becomes the reciprocal and we multiplied by a half so half becomes the power Remember half powers, the same thing A square root Finally hbr where do we see HBR? Luckily, we c h b r and only one place We see it right here as a product So they're both products so that's good. So there's no need to reverse but there's a two in front of that HBR So what do we need to do? We need to divide by two or same thing is multiplied by a half So this is gonna become half h two gas plus half br to gas gives me hbr Since I multiplied by half this is to the half power half powers, the same thing a square root. Okay, What we're gonna do next is we're gonna cross out intermediates things that look alike but our but is a product in one equation and are reacting in another. So we're gonna say here this h two is a product. This H two is a reactant. So they're going to cancel out this half Br two is a product, but this half br two is a reactant. They cancel out whatever doesn't get canceled. Out comes down. So what did you canceled out? H gas didn't get canceled out be our gas didn't get canceled out hbr gas and get canceled out and look, the equation we just isolated matches up with the equation above. Now all we have to do is we're gonna say K c four for missing equation equals K C one times k c two times k c three. So, basically, all we have to do here is we have to multiply each one of these right here. So multiply this times this times this multiplying all three of them will give us a K C four value of 4526. Hopefully, you guys were ableto follow along as we did this problem. Just realize the equation with the missing Casey value is the one we have to look at And we just looked compound by compound, look to see Where do we find them? In the given equations below When when were able to isolate them, you would just multiply all their K values together. And that will give us the overall K value for this equation we're looking for in the first place. So I just remember the tips that we did. If you reverse it, K becomes a reciprocal. If you multiplied by a number that becomes the power. If you divide by number, then it becomes one over that number as a power. So if you divided by five would be multiplying by 1/5. If you divided by four, it be like multiplying by 1/4. Those would become the powers. Just remember those small little principles, and you'll be able to get these questions correct.