Stoichiometry problems

Strategy Part (a) is essentially a stoichiometry problem of the type discussed in Chapter 4. For parts (b) and (c), start by calculating (1) the number of moles of OH added and then (2) the number of moles of H+ or OH- in excess. Finally, calculate (3) [H+] and pH. Remember to use the total volume of the solution at that point... 

This is a stoichiometry problem (how much ), in which we are asked to find the mass of a reactant. 

A table of amounts is a convenient way to organize the data and summarize the calculations of a stoichiometry problem. Such a table helps to identify the limiting reactant, shows how much product will form during the reaction, and indicates how much of the excess reactant will be left over. A table of amounts has the balanced chemical equation at the top. The table has one column for each substance involved in the reaction and three rows listing amounts. The first row lists the starting amounts for all the substances. The second row shows the changes that occur during the reaction, and the last row lists the amounts present at the end of the reaction. Here is a table of amounts for the ammonia example ... 

This is a stoichiometry problem involving gases. The mass of a product and the final pressure must be calculated. 

In any stoichiometry problem, work with moles. This problem involves gases, so use the ideal gas equation to convert P-V-T information into moles. 

This is an electrochemical stoichiometry problem, in which an amount of a chemical substance is consumed as electrical current flows. We use the seven-step strategy in summary form. The question asks how long the battery can continue to supply current. Current flows as long as there is lead(IV) oxide present to accept electrons, and the batteiy dies when all the lead(IV) oxide is consumed. We need to have a balanced half-reaction to provide the stoichiometric relationship between moles of electrons and moles of Pb02. 

The first step in any stoichiometry problem is to write the balanced chemical equation ... 

In a stoichiometry problem, (a) if the mass of a reactant is given, what conversions (if any) should be made (b) If a number of molecules is given, what conversions (if any) should be made (c) If a number of moles is given, what conversions (if any) should be made ... 

Make up your own stoichiometry problem using the equation... 

With molarity and volume of solution, numbers of moles can be calculated. The numbers of moles may be used in stoichiometry problems just as moles calculated in any other way are used. Also, the number of moles calculated as in Chap. 8 can be used to calculate molarities or volumes of solution. 

Equivalents are especially useful in dealing with stoichiometry problems in solution. Since 1 equivalent of one thing reacts with 1 equivalent of any other thing in the reaction, it is also true that the volume times the normality of the first thing is equal to the volume times the normality of the... 

In working stoichiometry problems you will need the balanced chemical equation. In addition, if the problem involves a quantity other than moles, you will need to convert to moles. 

The most important concept when working stoichiometry problems such as this one is moles. We must have moles to proceed. The mole determination of iodine will involve the molar mass of iodine (2 x 126.9 g/mol), while the mole determination of fluorine will involve Avogadro s number (since we have number of fluorine molecules). We can find the moles of each as follows ... 

In a molecular equation, we pretend that everything is a molecule (a nonelectrolyte). Molecular equations are quite useful when doing reaction stoichiometry problems. 

The first part of this problem appears in numerous problems involving solutions. Moles are critical to all stoichiometry problems, so you will see this step over and over again. This is so common, that anytime you see a volume and a concentration of a solution, you should prepare to do this step. 

We can use the gas law relationships, especially the ideal gas law and the combined gas law, in reaction stoichiometry problems. For example, suppose you have 2.50 g of an impure sample of KC103 and you want to determine how many grams of pure KC103 are present. You heat the mixture and the KC103 decomposes according to the equation ... 

Be sure, especially in stoichiometry problems involving gases, that you are calculating the values such as volume and pressure of the correct gas. You can avoid this mistake by clearly labeling your quantities that means, mol of 02 instead of just mol. 

Another type of gas law problem involves stoichiometry. Gas stoichiometry problems are just like all other stoichiometry problems—you must use moles. In addition, one or more gas laws are necessary. Let s look at a gas stoichiometry problem. What volume, in liters of oxygen gas, collected over water, forms when 12.2 g ofKCl03 decompose according to the following equation ... 

In this chapter, you learned about the properties of gases. You learned that you can use the combined gas law, the ideal gas law, or the individual gas laws to calculate certain gas quantities, such as temperature and pressure. You also learned that these equations could also be useful in reaction stoichiometry problems involving gases. You learned the postulates of the Kinetic-Molecular... 

Stoichiometry problems (including limiting-reactant problems) involving solutions can be worked in the same fashion as before, except that the volume and molarity of the solution must first be converted to moles. 

In stoichiometry problems, be sure to use the balanced chemical equation. 

Be able to work reaction stoichiometry problems using molarity. 

The gas law relationships can be used in reaction stoichiometry problems. For example, suppose you have a mixture of KC103 and NaCl, and you want to determine how many... 

Gas stoichiometry—Know how to apply the gas laws to reaction stoichiometry problems. 

The negative sign indicates that this reaction is exothermic. This value of AH is for the production of 2 mol of water. If 4 mol were produced, AH would be twice -483.6 kj. The techniques developed in working reaction stoichiometry problems (see the Stoichiometry chapter) also apply here. 

We need to calculate the amount of methyl tert-bu tyl ether that could theoretically be produced from 26.3 g of isobutylene and compare that theoretical amount to the actual amount (32.8 g). As always, stoichiometry problems begin by calculating the molar masses of reactants and products. Coefficients of the balanced equation then tell mole ratios, and molar masses act as conversion factors between moles and masses. 

Treat this as a typical stoichiometry problem to find the amount of diethyl ether that can theoretically be formed from 40.0 g of ethyl alcohol, and then multiply the answer by 87% to find the amount actually formed. 

Complex stoichiometry problems should be worked slowly and carefully, one step at a time. When solving a problem that deals with limiting reactants, the idea is to find how many moles of all reactants are actually present and then compare the mole ratios of those actual amounts to the mole ratios required by the balanced equation. That comparison will identify the reactant there is too much of (the excess reactant) and the reactant there is too little of (the limiting reactant). 

The relationship v/M XVj = MfX Vfis convenient for dilutions only. Students tend to use it for solution stoichiometry problems, which only works if file stoichiometry is 1 1. 

Solving stoichiometry problems always requires finding the number of moles of the first reactant, using the coefficients of the balanced equation to find the number of moles of the second reactant, and then finding the amount of the second reactant. The flow diagram in Figure 3.5 summarizes the situation. 

The sequence of conversions in Figure 18.20 is used to calculate the mass or volume of product produced by passing a known current through a cell for a fixed period of time. The key is to think of the electrons as a "reactant" in a balanced chemical equation and then to proceed as with any other stoichiometry problem. Worked Example 18.10 illustrates the calculations. Alternatively, we can calculate the current (or time) required to produce a given amount of product by working through the sequence in Figure 18.20 in the reverse direction, as shown in Worked Example 18.11. 

Synthesis of niobates and tantalates of alkaline metals at high temperatures may result in the products with unintended stoichiometry because of high volatility of alkaline metal (especially lithium) oxides. Therefore, their synthesis in the form of efficiently sintering powders presents a serious problem. Films of alkaline niobates and tantalates can find wide range of applications in acousto- and optoelectronics and are usually prepared by rf-sputtering techniques, also giving rise to stoichiometry problems. 

In reaction stoichiometry problems involving gases, the ideal gas law provides a means to compute moles from pressure or volume data. 

Since HC1 and NaOH are completely dissociated in dilute solutions, and the reaction goes to completion, this is really a simple stoichiometry problem in which we convert the HsO+ concentration to pH. If the initial... 

G. Quinkert, M. V. Kisakiirek (Eds) Reactivity Concepts for Oxidation Catalysis Spin and Stoichiometry Problems in Dioxygen Activation, Helvetica Chimica Acta, Zurich, 2001, pp. 131—156. 

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