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How to Calculate Theoretical Yields

❶Your answer will be a unit-less ratio.




Look at the balanced equation for the reaction. The coefficients in front of each molecule tell you the ratio of the molecules that you need for the reaction to occur.

If you use exactly the ratio given by the formula, then both reactants should be used equally. The coefficients indicate that you need 6 oxygen molecules for every 1 glucose molecule. Compare the ratios to find the limiting reactant. In most chemical reactions, one of the reactants will be used up before the others. The one that gets used up first is called the limiting reactant. This limiting reactant determines how long the chemical reaction can take place and the theoretical yield you can expect.

Compare the two ratios you calculated to identify the limiting reactant: The formula tells you that your ideal ratio is 6 times as much oxygen as glucose.

Therefore, you have more oxygen than required. Thus, the other reactant, glucose in this case, is the limiting reactant.

Review the reaction to find the desired product. The right side of a chemical equation shows the products created by the reaction. The coefficients of each product, if the reaction is balanced, tells you the amount to expect, in molecular ratios. Each product has a theoretical yield, meaning the amount of product you would expect to get if the reaction is perfectly efficient. The two products shown on the right are carbon dioxide and water.

You can begin with either product to calculate theoretical yield. In some cases, you may be concerned only with one product or the other. If so, that is the one you would start with. Write down the number of moles of your limiting reactant. You must always compare moles of reactant to moles of product.

If you try to compare the mass of each, you will not reach the correct results. The molar mass calculations found that the initial 25g of glucose are equal to 0.

Compare the ratio of molecules in product and reactant. Return to the balanced equation. Divide the number of molecules of your desired product by the number of molecules of your limiting reactant. In other words, this reaction can produce 6 molecules of carbon dioxide from one molecule of glucose.

Multiply the ratio by the limiting reactant's quantity in moles. The answer is the theoretical yield, in moles, of the desired product. In this example, the 25g of glucose equate to 0. The ratio of carbon dioxide to glucose is 6: You expect to create six times as many moles of carbon dioxide as you have of glucose to begin with.

The theoretical yield of carbon dioxide is 0. Convert the result to grams. This is the reverse of your earlier step of calculating the number of moles or reactant. When you know the number of moles that you expect, you will multiply by the molar mass of the product to find the theoretical yield in grams.

The theoretical yield of the experiment is Repeat the calculation for the other product if desired. In many experiments, you may only be concerned with the yield of one product. If you wish to find the theoretical yield of both products, just repeat the process. According to the balanced equation, you expect 6 molecules of water to come from 6 molecules of glucose.

This is a ratio of 1: Therefore, beginning with 0. Multiply the number of moles of water by the molar mass of water. Multiplying by the product, this results in 0.

The theoretical yield of water for this experiment is 2. Doesn't one molecule of glucose produce six molecules of water, not one? Not Helpful 0 Helpful 2. Your final step with the image you provided does not match.

Is the theoretical mass of water 15 grams or 2. For solids, divide the mass of a reactant used by its molecular weight. For liquids and gases, multiply the volume by the density and then divide by the molecular weight. Multiply the molecular weight by the number of moles in the equation.

The reactant that has the smallest mole number is the limiting reagent. Calculate the theoretical mole yield by using the chemical equation. The multiply the ratio between the limiting reagent and the product by the number of moles of the limiting reagent used in the experiment. Multiply the number of moles of the product by the molecular weight of the product to determine the theoretical yield. For example, if you created 0. Mark Kennan is a writer based in the Kansas City area, specializing in personal finance and business topics.

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Use molar mass of reactant to convert grams of reactant to moles of reactant. Use the mole ratio between reactant and product to convert moles reactant to moles product. Use the molar mass of the product to convert moles product to grams of product.

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Knowing the theoretical yield helps determine a reaction's efficiency. This is important to know at any level, from beginning chemistry students to industrial chemists seeking to .

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The theoretical yield is the amount of the product in g formed from the limiting reagent. From the moles of limiting reagent available, calculate the grams of product that is theoretically possible (same as Step 4 above). To determine theoretical yield, multiply the amount of moles of the limiting reagent by the ratio of the limiting reagent and the synthesized product and by the molecular weight of the product. Example: Theoretical Yield.

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Theoretical Yield Example If g of HCl are reacted with g of CaCO3, according to the following balanced chemical equation, calculate the theoretical yield of CO2. 2HCl+CaCO3 →CaCl2 +H2O+CO2 1. Determine the number of moles of one of the products (CO2 in this example) produced if all. Since the actual amount of product is often less than the theoretical yield, chemists also calculate the percent yield using the ratio between the experimental and theoretical yield. [Attributions and references].