Calculations limiting reactant determination

STRATEGY First, the limiting reactant must be identified (Toolbox M.l). This limiting reactant determines the theoretical yield of the reaction, and so we use it to calculate the theoretical amount of product by Method 2 in Toolbox L.l. The percentage yield is the ratio of the mass produced to the theoretical mass times 100. Molar masses are j calculated using the information in the periodic table inside the front cover of this i book. 

Write a balanced chemical equation for the reaction. Find the amount (in mol) of each reactant, using its volume and concentration. Identify the limiting reactant. Determine the amount (in mol) of mercury(II) sulfide that forms. Calculate the mass of mercury(II) sulfide that precipitates. 

In cases where the reactants involved are not present in the proper stoichiometric ratios, the limiting reactant will have to be determined and the excess amounts of the other reactants calculated. It is safe to assume that unconsumed reactants and inert components exit with the products in their original forms. Consider the following example. 

Often you will be given the amounts of two different reactants and asked to determine which is the limiting reactant, to calculate the theoretical yield of the product and to find how much of the excess reactant is unused. To do so, it helps to follow a systematic, four-step procedure. 

In some cases, we must determine by calculation which is the limiting reactant. For example, from the equation... 

A reaction that is carried out under limiting reactant conditions nevertheless has a yield that generally will be less than 100%. The reasons why reactions yield less than the theoretical amounts, given in Section 4-1. apply to all reactions. When a reaction operates under limiting reactant conditions, we calculate the theoretical yield assuming that the limiting reactant will be completely consumed. We then determine the percent yield as described in Section 4A. Example shows how to do this. 

The problem asks for a yield, so we identify this as a yield problem. In addition, we recognize this as a limiting reactant situation because we are given the masses of both starting materials. First, identify the limiting reactant by working with moles and stoichiometric coefficients then carry out standard stoichiometry calculations to determine the theoretical amount that could form. A table of amounts helps organize these calculations. Calculate the percent yield from the theoretical amount and the actual amount formed. 

The quantitative treatment of a reaction equilibrium usually involves one of two things. Either the equilibrium constant must be computed from a knowledge of concentrations, or equilibrium concentrations must be determined from a knowledge of initial conditions and Kgq. In this section, we describe the basic reasoning and techniques needed to solve equilibrium problems. Stoichiometry plays a major role in equilibrium calculations, so you may want to review the techniques described in Chapter 4, particularly Section 4- on limiting reactants. 

For the rest of the exercise, the plan is straightforward for the neutralization reaction between HN03 and NaOH, perform the limiting reactant problem. The pH is determined from the concentration of excess HN03 or NaOH. Each calculation is totally independent of the other calculations. 

Before the equivalence point, the pH is determined by the buffer solution consisting of the unreacted CH3COOH and NaCH3COO produced by the reaction. Each calculation is a limiting reactant problem using the original concentration of CH3COOH. 

First of all, we have to determine which the limiting reactant is. The way to determine which reactant is limiting is to divide the moles of each reactant by the coefficient from the balanced equation associated with that reactant. The smallest number that comes out indicates which reactant is the limiting one. This reactant limits how much of every other species made or needed for the reaction. For A, this calculation gives 0.25 and for B, 0.5. Thus, A is the limiting reactant and the calculation of d, sR, and x should based on it. 

Fe(l) + Al203(s). (a) Which is the limiting reactant (b) Determine the maximum amount of iron (in moles of Fe) that can be produced, (c) Calculate the mass of excess reactant remaining in the crucible. 

The amount of product is calculated by the same method used earlier for mole-to-gram stoichiometry problems. Start with the moles of the limiting factor because a limiting factor is defined as the reactant that limits or determines the amount of product that can be made. 

To determine the limiting reactant, you can calculate how much of either ammonia or lithium hydroxide would be produced by the reactants. In this problem, ammonia was chosen because only one mole is produced, simplifying the calculation. 

Since chemical reactions usually occur with one or more of the reactants in excess, you often need to determine the limiting reactant before you carry out stoichiometric calculations. You can incorporate this step into the process you have been using to solve stoichiometric problems, as shown in Figure 7.7. 

In what cases would it not be necessary to determine the limiting reactant before beginning any stoichiometric calculations ... 

Using a concept map, explain how to calculate the number of grams of C that can be obtained when a given mass of A reacts with a certain number of molecules of B. Assume that you know the molar mass of A and C. Include proper units. For simplicity, assume that A is limiting, but don t forget to show how to determine the limiting reactant. 

By convention, the amount of excess reactant in a reaction is always defined on the basis of the reaction going to 100 percent completion for the limiting reactant. The degree of completion is not a factor in determining or specifying the excess of reactants. For example, if methane is burned with 10 percent excess air, the volume of air needed to burn the methane is calculated as though there is total combustion of methane to carbon dioxide and water. 

For problems in which the quantities of two (or more) reactants are given, we must determine if one of the reactants is present in a quantity less than, equal to, or greater than that required to react with all the other reactants. Determine which reactant is in limiting quantity and use that quantity to calculate the quantities of the substances that will be used up and produced. A table of reactant and product quantities is useful. If masses are... 

If, however, 2.50 X 103 kilograms of methane is mixed with 3.00 X 103 kilograms of water, the methane will be consumed before the water runs out. The water will be in excess. In this case the quantity of products formed will be determined by the quantity of methane present. Once the methane is consumed, no more products can be formed, even though some water still remains. In this situation, because the amount of methane limits the amount of products that can be formed, it is called the limiting reactant, or limiting reagent. In any stoichiometry problem it is essential to determine which reactant is the limiting one to calculate correctly the amounts of products that will be formed. 

Note that to determine the limiting reactant, we could have started instead with the given amount of hydrogen and calculated the moles of nitrogen required ... 

There was 0.30 mol of SrCl2 in every liter of solution. Calculate the number of moles of SrCl2 that were added. Determine whether SrCl2 or Na2C03 was the limiting reactant. Would this experiment have worked if the other reactant had been chosen as the limiting reactant Explain why or why not. 

The calculations you did in Section 12.2 were based on having the reactants present in the ratio described by the balanced chemical equation. How can you calculate the amount of product formed when one reactant limits the amount of product and the other is in excess The first thing you must do is determine which reactant is the limiting reactant. 

After the limiting reactant has been determined, the amount of product in moles can be calculated by multiplying the given number of moles of the limiting reactant (1.410 mol CI2) by the mole ratio that relates disulfur dichloride and chlorine. 

There is a systematic method to find the limiting reactant and determine the maximum possible amounts of products. Take each reactant in turn, assume that it is used up completely in the reaction, and calculate the mass of one of the products that will be formed. Whichever reactant gives the smallest mass of this product is the limiting reactant. Once it has reacted fully, no further product can be formed. 

Given a set of initial masses of reactants and a balanced chemical equation, determine the limiting reactant and calculate the masses of reactants and products after the reaction has gone to completion (Section 2.6, Problems 47 and 48). 

As a shortcut to determining the limiting reactant, all you have to do is to calculate the mole ratio(s) of the reactants and compare each ratio with the corresponding ratio of the coefficients of the reactants in the chemical equation thus ... 

For multiple reactions with reactants participating in more than one reaction, it is more difficult to determine the limiting reactant and often it is necessary to calculate the concentration as the reactions proceed to determine which reactant is consumed first. When the limiting reactant is depleted, all reactions that use this component as reactant stop, and the corresponding rates become zero. 

We are given masses of both CH4 and O2, so we calculate the number of moles of each reactant, and then determine the number of moles of each reactant required to react with the other. From these calculations we identify the limiting reactant. Then we base the calculation on it. 

Determining Chemical Formulas Calculations in Chemical Reactions Limiting Reactants... 

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