ava asked in Science & MathematicsChemistry · 2 months ago

So if I'm trying to find the limiting reagent in a chemical equation, and there are two products, which product do I use in the mole ratio with both the reactants? Like for example, why would I do the mole ratio with AlCl3 in the equation 2Al(s) + 3CuCl2(aq) -> 3Cu(s) + 2AlCl3(aq)?

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• Anonymous
1 month ago

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• david
Lv 7
2 months ago

Use either --- both will end up giving the same limiting reactant. ===  Actually you do not need to use either, but I don't want to confuse you by showing you something easier ... well, I'll give it a try.

I'll use your ex. and ust make up a problem to show you.

15.4 g  Al is reacted with 40.5 g CuCl2 ... What is the limiting reactant?

Convert mass to moles

15.4 / 27  =  0.5704 mole Al

40.5 / 135  =  0.300 mole CuCl2

make a ratio .. divide and get a decimal

Al / CuCl2  =  0.5704/0.300 = 1.90

use the same to make a mole ratio from the eq.

Al / CuCl2  =  3/2  =  1.5

If the larger is the ratio from the problem, then the top substance in the ratio is the EXCESS.  If the ratio from the problem is less then the TOP SUBSTANCE is the limiting reactant.

1.90 > 1.5  so Al is the excess, and CuCl2 is the limiting reactant.

• Anonymous
2 months ago

You only consider the reactants in determining the limiting reactant.

Let's say you have 1 mole of each.

Per the equation, 1 mole of Al needs 1.5 moles of CuCl2.  You only  have 1 mole of CuCl2 so it is the limiting reactant.

You get the same answer if you consider how much Al reacts with 1 mole of CuCl2.  per the equation, 1 mole of CuCl2 reacts with 2/3 moles of Al.  Since you have more Al than that, CuCl2 is again the limiting reactant.