Volume Relationships in Reactions Involving Gases

12-12 Mass-Volume Relationships in Reactions Involving Gases 

Many chemical reactions produce gases. For instance, the combustion of hydrocarbon in excess oxygen at high temperatures produces both carbon dioxide and water as gases, as illustrated for octane. 

The N2 gas produced by the very rapid decomposition of sodium azide, NaN3(s), inflates air bags used as safety devices in automobiles. 

We know that one mole of gas, measured at STP, occupies 22.4 liters we can use the ideal gas equation to find the volume of a mole of gas at any other conditions. This information can be utilized in stoichiometry calculations (see Section 3-2). 

Small amounts of oxygen can be produced in the laboratory by heating solid potassium chlorate, KCIO3, in the presence of a catalyst, manganese(TV) oxide, Mn02- Solid potassium chloride, KCl, is also produced. 

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Charles s Law The Volume-Temperature Relationship The 12-12 Mass-Volume Relationships in Reactions Involving Gases... 

MASS-VOLUME RELATIONSHIPS IN REACTIONS INVOLVING GASES... 

Dalton s Law of Partial Pressures 12-12 Mass-Volume Relationships in Reactions Involving Gases 12-13 The Kinetic-MolecularTheory 12-14 Diffusion and Effusion of Gases 12-15 Deviations from Ideal Gas Behavior... 

In reactions involving gaseous reactant or products, we often specify the quantity of a gas in terms of its volume at a given temperature and pressure. As we have seen, stoichiometry involves relationships between amounts in moles. For stoichiometric calculations involving gases, we can use the ideal gas law to determine the amounts in moles from the volumes, or to determine the volumes from the amounts in moles. 

The law of combining volumes, like so many relationships involving gases, is readily explained by the ideal gas law. At constant temperature and pressure, volume is directly proportional to number of moles (V = kin). It follows that for gaseous species involved in reactions, the volume ratio must be the same as the mole ratio given by the coefficients of the balanced equation. 

You have already learned that the ideal gas law can be used to solve for different variables in several different types of situations. As you may recall, the term stoichiometry" refers to the relationship between the number of moles of the reactants and the number of moles of the products in a chemical reaction. In this section, you will learn how to use Gay-Lussac s law of combining volumes and the ideal gas law to solve stoichiometric problems that involve gases. 

When we discussed quantitative aspects of chemical reactions in Chapter 4, we emphasized the importance of ratios of moles. The ideal gas law provides a relationship between the number of moles of a gas and some easily measurable properties pressure, volume, and temperature. So when gases are involved in a chemical reaction, the ideal gas law often provides the best way to determine the number of moles. Using the ideal gas law in a stoichiometry problem really doesn t involve any new ideas. It just combines two kinds of calculations that you ve already been doing. We ll still do the stoichiometric calculation in terms of mole ratios, as always, and we ll use the gas law to connect the number of moles of a gas with its temperature, pressure, and volume. 

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