In-Class Limiting Reactant and Theoretical Yield Problem  [ENDORSED]

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Bree Perkins 1E
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Joined: Fri Apr 06, 2018 11:04 am

In-Class Limiting Reactant and Theoretical Yield Problem

Postby Bree Perkins 1E » Sat Apr 07, 2018 2:19 pm

Hi Everyone, I have a question on the last problem that the professor did on Friday in week one. The problem was: Solid Calcium Carbide CaC2 reacts with H2O to for aqueous Calcium Hydroxide, Ca(OH)2 and Ethyne gas C2H2. What is the limiting reactant when 100g H2O reacts with 100g CaC2? What is the theoretical yield of ethyne in grams?

I understand that because of the 1 to 1 ratio of CaC2 to C2H2, you will get 1.56 moles of C2H2, but my question is that what if the ratio was 1 to 2 instead of one to one? Would you still get 1.56 moles of C2H2 because it depends on the limiting reactant, or would it be a different number?

Betty Wolkeba section 1L
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Joined: Fri Apr 06, 2018 11:05 am

Re: In-Class Limiting Reactant and Theoretical Yield Problem

Postby Betty Wolkeba section 1L » Sat Apr 07, 2018 4:01 pm

I believe that it would still be the same because essentially, the limiting reactant determines the maximum amount of how much a product would be produced. However, someone should reassert this.

Tiffany Chen 1A
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Re: In-Class Limiting Reactant and Theoretical Yield Problem

Postby Tiffany Chen 1A » Sat Apr 07, 2018 4:53 pm

In this particular problem, I think it's kind of confusing to think about the ratio of CaC2 to C2H2 as 1:2 instead of 1:1 because that would make the equation unbalanced. But if you had a different chemical equation where the ratio of the limiting reactant to the product the question referred to was 1:2, and you had 1.56 mol of the limiting reactant, I think you would produce 2(1.56) = 3.12 mol of that product, not 1.56 mol.
The idea that the amount of product depends on the amount of the limiting reactant doesn't mean that the amount of mols of the limiting reactant equals the mols of the product in question, so the ratio should still apply.

[someone please correct me if I'm wrong, because I'm not confident in my reasoning]

Chem_Mod
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Re: In-Class Limiting Reactant and Theoretical Yield Problem  [ENDORSED]

Postby Chem_Mod » Sat Apr 07, 2018 5:03 pm

"But if you had a different chemical equation where the ratio of the limiting reactant to the product the question referred to was 1:2, and you had 1.56 mol of the limiting reactant, I think you would produce 2(1.56) = 3.12 mol of that product"

Correct. Good answer.

The ratios always apply that is why I spent a good deal of time balancing chemical equations in class.

Remember we balance chemical equations due to conservation of mass in a chemical reaction:

mass reactants = mass products

Therefore,

total of all atom types in reactants = total of all atom types in products


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