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01:47 University of Maine

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Problem 54

In the process of balancing the equation
$$\mathrm{Al}+\mathrm{Cl}_{2} \longrightarrow \mathrm{AlCl}_{3}$$
Student I writes: Al $+\mathrm{Cl}_{2} \longrightarrow \mathrm{AlCl}_{2}$
Student II writes: $\mathrm{Al}+\mathrm{Cl}_{2}+\mathrm{Cl} \longrightarrow 2 \mathrm{AlCl}_{3}$
Student III writes: $2 \mathrm{Al}+3 \mathrm{Cl}_{2} \longrightarrow 2 \mathrm{AlCl}_{3}$
Is the approach of Student I valid? Student II? Student III?
Explain.

Student I: No; Student II: No; Student 3: Yes

## Discussion

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## Video Transcript

in balancing a chemical equation, The identity of the reactant and products are given, and the only information that you can change are the mole ratios. The mole ratios are the coefficients that are numbers that come in front of each of the substances. So if I have to balance this reaction where I have a l plus seal to make a l. C. +03 I can't change any of these substances. But if you look at it, it's not balanced. There's one aluminum here, and there are two. Chlorine is here on this side. There's only there's one aluminum. There are three Korans. So the question is, how do I get another chlorine on this side? So the first student proposes changing to make a balanced equation where there's one aluminum and one aluminum to chlorine and to Clarins. But this isn't possible because I've changed the identity of the product. The equation that I'm given says that I'm making a LCL three, so this has to be a LSI L three student to propose is bouncing the equation by adding an additional chlorine Adam here, and it is balanced. One aluminum, one aluminum, three chlorine and three but I've added an additional substance, which I can't dio. The third student changes the ratio of each substance, so they have two moles of aluminum. Reacts with three moles of chlorine to make two moles of ale si l three. So I haven't changed anything from my original skeleton. And if we look at it, there are two ales, six seals on this side and on this side there to Ailes and six seals. So it's balanced and it's balanced because it has equal numbers of each Adam on both sides and the identity of the reactant and products have stayed the same. So when you balance equation, the only thing that you can change are the coefficients or the numbers that come in front of each substance.