Calculating grams of product from moles

SECTIONS 3.6 AND 3l7 The mole concept can be used to calculate the relative quantities of reactants and products in chemical reactions. The coefficients in a balanced equation give the relative numbers of moles of the reactants and products. To cakulate the number of grams of a product from the number of grams of a reactant, first convert grams of reactant to moles of reactant. Then use the coefficients in the balanced equation to convert the number of moles of reactant to moles of product. Finally, convert moks of product to grams of product. 

Again, we find the limiting reactant by calculating how much product can be made from each reactant. Since we are given the initial amoimts in grams, we must first convert to moles. After we convert to moles of product, we convert back to grams of product. The reactant that makes the least amount of product is the limiting reactant. 

The quantities of the reactants can also be given in grams. The calculations to identify the limiting reactant are the same as before, but the grams of each reactant must first be converted to moles, then to moles of product, and finally to grams of product. Then select the smaller mass of product, which is from complete use of the limiting reactant This calculation is shown in Sample Problem 9.6. 

This balanced equation can be read as 4 iron atoms react with 3 oxygen molecules to produce 2 iron(III) oxide units. However, the coefficients can stand not only for the number of atoms or molecules (microscopic level) but they can also stand for the number of moles of reactants or products. So the equation can also be read as 4 mol of iron react with 3 mol of oxygen to produce 2 mol ofiron(III) oxide. In addition, if we know the number of moles, the number of grams or molecules may be calculated. This is stoichiometry, the calculation of the amount (mass, moles, particles) of one substance in the chemical equation from another. The coefficients in the balanced chemical equation define the mathematical relationship between the reactants and products and allow the conversion from moles of one chemical species in the reaction to another. 

You are given the mass of the reactant AgNOj and the actual yield of the product Ag2Cr04. You need to write the balanced chemical equation and calculate the theoretical yield by making these conversions grams of silver nitrate to moles of silver nitrate, moles of silver nitrate to moles of silver chromate, moles of silver chromate to grams of silver chromate. The percent yield can be calculated from the actual yield of product and the calculated theoretical yield. 

Whether the units given for reactants (or products) are moles, grams, liters (for gases), or some other units, we use moles to calculate the amount of product formed in a reaction. This approach is called the mole method, which means simply that the stoichiometric coefficients in a chemical equation can be interpreted as the number of moles of each substance. For example, industrially ammonia is synthesized from hydrogen and nitrogen as follows ... 

Calculate the amount of product (moles or grams, as needed) formed from each reactant. 

We know the mass of sample (0.312 6 g), so we need to find the mass of piperazine. The experiment gives us the mass of the product piperazine diacetate (0.712 1 g) made from piperazine. How much piperazine is contained in 0.712 1 g of piperazine diacetate Each mole of piperazine diacetate contains one mole of piperazine in Reaction 7-1. If we compute the moles of piperazine diacetate product, we can find the moles of piperazine in the sample. From the moles of piperazine, we can calculate the grams of piperazine and its weight percent. 

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