Q&A for How to Calculate Theoretical Yield

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Doesn't one molecule of glucose produce six molecules of water, not one?

Community Answer

Yes. One molecule of glucose plus six molecules of oxygen = six molecules of water plus six molecules of carbon dioxide.

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What should I do if there is more than one reactant?

Community Answer

Find out which of the reactants is the "limiting" reactant and use that to calculate the theoretical yield. This can be done using Part 1 of this article.

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What should I do if the reactants have the same number of moles?

Hannah

Community Answer

That's not a problem! It only means that the molar ratio of your reactants is 1. In the next step, you need to compare it to the ideal molar ratio from your chemical equation to find the limiting reactant and continue as described in the article.

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What should i do if both of the reactants are limiting?

Hannah

Community Answer

This means that the molar ratio of your reactants is equal to the ideal molar ratio. You just skip the "limiting reactant" step and can choose either reactant to compare the ratio of molecules in the product and reactant - it will give you the same result. So for example, if you have 2 mole of glucose and 12 moles of oxygen, there are two ways to find the yield of carbon dioxide: 1. 1 glucose molecule makes 6 CO2 molecules (you multiply by 6) - therefore 2 moles of glucose makes 12 moles of CO2. 2. 6 O2 molecules make 6 CO2 molecules (you multiply by 1). Therefore, 12 moles of O2 make 12 moles of CO2.

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Can the theoretical yield be higher than the total mass of the reactants?

Hannah

Community Answer

No, as this would violate the law of conservation of mass. The law states that in a closed system, the mass must be constant over time. The mass of the reactants will be lower but the mass of the product will become greater by the same amount. But be careful to include all reactants - don't forget about gases (if iron wool is burned, it becomes heavier due to the oxygen involved)!

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