Theoretical yield: confused

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Ariana Flores 3F
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Theoretical yield: confused

Postby Ariana Flores 3F » Sat Oct 10, 2020 6:41 pm

I am a bit confused by what theoretical yield actually is. In the Wednesday week 1 lecture, Dr. Lavelle says the theoretical yield is the "100%" and ideal yield, however, in step 7 of "Identifying a Limiting Reactant" we are supposed to convert moles of product to grams. He then says the "difference" between the calculated moles of the product possible (Step 6) and the moles calculated in step 7.

I just don't understand how the theoretical yield is supposed to be the "ideal/100%" but in order to find it, we take the difference of product possible and the molar mass of the product.

I think that I am a bit confused here in general but I hope my question made sense.


Brennan McGurrr 3C
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Re: Theoretical yield: confused

Postby Brennan McGurrr 3C » Sat Oct 10, 2020 6:53 pm

I think I understand your question. Theoretical yield has to do with calculations and is like a best case scenario. The actual yield would be equal to the theoretical yield if all of the limiting reactant perfectly underwent the reaction. This never happens in the lab, so the actual yield is always less. In order to find theoretical yield, you would have to do stoichiometry, using molar masses and molar ratios. Percent yield is a measure of how close the reaction was to perfect. I hope this helps.

Jonathan Banh 1G
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Re: Theoretical yield: confused

Postby Jonathan Banh 1G » Sat Oct 10, 2020 7:09 pm

To help clarify, the preliminary aspect of theoretical versus actual yield is that theoretical yield is the maximum, PERFECT amount of product that you can gain from a reaction while actual yield is the practical, REALISTIC amount of product gained from a reaction after legitimate experimentation in a lab. Remember that there are many things that happen during a reaction that contribute to an imperfect yield, such as heat loss and whatnot, making the conditions necessary for theoretical yield virtually impossible to satisfy. Theoretical yield is calculated using the known weight of the reactants and their molar mass to predict the amount of product that could be formed. If there is a limiting reactant(s), then the molecular weight of the (most) limiting reactant would be used as the basis to find the amount of product possible. The overarching idea of theoretical yield is that in chemistry, the calculations used to find it simply paint a preliminary picture of what could happen, but do not account for other factors that may lead to lower product yield. I think what you are confused upon is perhaps a minor conflict with terminology, referring to the percent yield formula instead. Instead of difference, think of percent yield as the quotient of the molecular weight of the product that was measured after an experiment and the hypothetical molecular weight of the product that the reaction could have produced under perfect conditions. Hence the percent yield formula, (Actual Yield/Theoretical Yield)(100). Percent yield is not to be confused with actual or theoretical yield. It is actually the true outcome of the reaction, or in other words, the percentage of the theoretical yield that the actual yield fulfilled or lived up to. If you are still confused, I would be happy to continue to follow up with you! Don't worry! This is confusing, yet crucial concept so it is great that you asked such a question!

Joshua Swift
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Re: Theoretical yield: confused

Postby Joshua Swift » Sat Oct 10, 2020 8:26 pm

The theoretical yield is basically what you would end up with if you did a reaction in a perfect world. This means all of your numbers would be 100% spot on with no human error. Because there is no way around human error in a real experiment, we have the theoretical yield which we calculate based on equations, masses, etc. and the actual yield which is the result we reach with the small errors which are naturally made along the way. We then use both of these to calculate the percent error in our experiments.

Isabelle Hales 1J
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Re: Theoretical yield: confused

Postby Isabelle Hales 1J » Sun Oct 11, 2020 9:57 am

The theoretical yield is the maximum amount of product that can be produced if everything goes perfectly (no residue left behind, no side reactions, etc.). In order to find the theoretical yield, you use the moles of the limiting reactant. This may be causing some confusion because even if you have large amounts of other reactants that would seem to result in a lot of product formed, the limiting reactant will ultimately make the amount of product much smaller.

I like to think about Dr. Lavelle's analogy of parts for a car. You are assembling cars and you have many car parts (steering wheels, engines, etc). However, you only have 8 tires. Even though you have enough other car parts to make at least 10 cars, the 8 tires will limit how many cars you will produce. In this case, the theoretical yield would be 2 cars (because each car needs 4 tires).

Nick P 3D
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Re: Theoretical yield: confused

Postby Nick P 3D » Sun Oct 11, 2020 1:05 pm

I think you may have gotten confused by the difference between percent yield and theoretical yield. Theoretical yield provides a mathematically created estimate of an experiment's results in an ideal world. Basically, it shows what your yield would be without any of the real world factors such as human error that can affect your experiment. Percent yield, on the other hand, simply compares this theoretical yield to the actual amount of product when the experiment was performed in real life, where the factors excluded from theoretical yield come into play.

Melissa Solis 1H
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Re: Theoretical yield: confused

Postby Melissa Solis 1H » Sun Oct 11, 2020 2:01 pm

Like everyone here has replied, the theoretical yield is just your ideal yield. Additionally, your actual yield should be less than the theoretical yield since the reactions can stick onto the testing tube, etc. Hope this makes sense!

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Re: Theoretical yield: confused

Postby 605291562 » Sun Oct 11, 2020 4:05 pm

Yes like others have said theoretical yield is assuming that there is no mass lost due to error (like sticking to the tube, etc.) When you compare the theoretical yield to what was actually produced you are most likely finding the percent yield.

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Re: Theoretical yield: confused

Postby Gustavo_Chavez_1K » Sun Oct 11, 2020 4:16 pm

Yeah I completely understand too as I have also been confused on the theoretical and actual yield. So I did some minor research and the theoretical yield is essential the amount of product made if there were no errors made. This is basically impossible though due to side reactions and other things that were stated in lecture. That is why we use the difference of the products possible and the molar mass, so that we can get the maximum amount of grams (or theoretical yield). The actual yield is how much product is actually attained considering the small errors and side reactions. So we use both the actual yield and the theoretical yield to find the percent yield which basically describes the percentage of error.

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