Volume law of combining

Perhaps the first stoichiometric relationship to be discovered was the law of combining volumes, proposed by Gay-Lussac in 1808 The volume ratio of any two gases in a reaction at constant temperature and pressure is the same as the reacting nude ratio. 

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. 

Avogadro suggested this relationship to explain the law of combining volumes. Today it seems obvious. For example, in the reaction... 

In order to work out reacting volumes of gases, we can use Gay-Lussac s law of combining volumes When gases react they do so in volumes which bear a simple ratio to each other and to the volumes of the products if they are gases, all measurements of volume being at the same temperature and pressure . 

B Here we are not dealing with gaseous reactants the law of combining volumes cannot be used. From the ideal gas equation we determine the amount of N2(g) per liter under the specified conditions. Then we determine the amount of Na(l) produced simultaneously, and finally the mass of that Na(l). 

A The law of combining volumes permits us to use stoichiometric coefficients for volume ratios. 

Professor of chemistry at the ficole Poly-technique and at the Jardin des Plantes. With Thenard, he prepared potassium without the use of a battery, and isolated boron. In 1809 Gay-Lussac enunciated his famous law of combining volumes of gases. 

Joseph Louis Gay-Lussac, Memoir on the combination of gaseous substances with each other, [1809]. Quoted in Leicester and Klickstein, Source Book in Chemistry, 298. See M.R Crosland, The origins of Gay-Lussacs law of combining volumes, Ann. Sci, 17 (1961) 1-26. 

Boyle (1662) observed that at constant temperature the volume of a sample of gas varies inversely with pressme, but Boyle did not explain why this was so. Somewhat later. Charles (1787) refined the observation to the effect that the volume of any sample of a gas vanes directly with the absolute temperature provided thal the pressure is held constant. A few years later, Gay-Lussac (1808), in reporting the results of his experiments with reacting gases, observed that volumes of gases that are used or produced in a chemical reaction can be expressed in ratios of small whole numbers—a concept to become known as Gay-Lussac s law of combining volumes. It should be noted that tlie foregoing concepts proposed by Boyle, Charles, and Gay-Lussac were based upon experimental observations, not on theory. 

Historically, the observation that volumes of reacting gases always simplified to ratios of small, whole numbers is called Gay-Lussac s Law of Combining Volumes. In the preceding example, the volumes of NO to 02 to N02 fit the pattern of 2 1 2. This observation further strengthened Dalton s argument for an atomic theory of matter. 

French chemist and physicist Joseph-Louis Gay-Lussac, who published the Law of Combining Volumes of Gases. ... 

In 1808 Gay-Lussac published his Law of Combining Volumes of Gases. He determined that when different gases reacted, they would always do so in small whole number ratios (e.g., two volumes of hydrogen would react with one volume of oxygen in forming H20). This was one of the greatest advancements of its time and helped form the basis for later atomic theory and how chemical reactions occur. 

Joseph Louis Gay-Lussac developed the gas law stating that gas pressure is directly proportional to absolute temperature. He also determined that 2 volumes of hydrogen react with one of oxygen to produce water and that other reactions occurred with similar simple ratios. These observations led him to develop the Law of Combining Volumes. 

Gay-Lussac s Law of Combining Volumes. The measurement of the volumes of gases which enter into chemical reaction led Gay-Lussac to perceive the existence of an extremely simple relationship which is known by the above title and which may be stated as follows The volumes of gases which react chemically are in the ratio of small whole numbers. Furthermore, if the products of the reaction are also gaseous their volumes are also in the relation of small whole numbers to each other and to the volumes of the original gases. 

His research led him to devise the law of combining volumes When gases react, the volumes of the reactants and the products, measured at equal temperatures and pressures, are always in whole number ratios. For example, 2 volumes of hydrogen gas react with 1 volume of oxygen gas to produce 2 volumes of water vapour. 

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. 

This information will help you with a certain type of gas stoichiometry problem. When a gas reacts to produce another gas, you can use Gay-Lussac s law of combining volumes to find the volumes of the gases. The following Sample Problem shows you how. 

O fii Gay-Lussac s law of combining volumes provides a short-cut for some gas calculations. What type of gas reaction lets you use this law ... 

Italian chemist and physicist Amadeo Avogadro (1776-1856) proposed a correct molecular explanation for Gay-Lussac s law of combining volumes. His work provided a simple way to determine atomic weights and molecular weights of gases. 

Subsequent research proved that Gay-Lussac s Law of Combining Volumes is not exact, but only an approximation,4 so that oxygen and hydrogen do not behave as perfect gases. For an accurate calculation of the relative values for the atomic weights of hydrogen and oxygen, it is therefore essential to know not only the relative densities of the... 

The law of combining volumes contributed to the understanding that the elemental gases H2, N2, O2, F2, and CI2 are diatomic. For example, consider the reaction of H2 and CI2. We write the reaction today as... 

In 1800, chemists did not know that the elementary gases were diatomic, and they wondered how two molecules of HCl were formed from one molecule of H and one of Cl. The law of combining volumes led Amedeo Avogadro (1776-1856) to postulate in 1811 a hypothesis that equal volumes of gases under like conditions of temperature and pressure contain equal numbers of molecules. The fact that molecules of hydrogen and chlorine had to be diatomic stemmed from this generalization. 

Gay-Lussac s law of combining volumes relates the volumes of gases involved in a reaction, all measured separately at the same temperature and pressure. The volume ratio under these conditions is equal to the mole ratio and, therefore, to the ratio of coefficients in the balanced chemical equation (Section 12.9). 

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