Definite proportion

Atoms combine in definite proportions to give molecules. For example, natural gas is mostly composed of methane, a substance in which four hydrogen atoms (H) are combined with one carbon (C) the molecular formula is written as CH4. Similarly, water, ammonia, ethanol, and glucose have... 

In Figure 10.19a, no new compound was formed between the solute and solvent. Some solutes can form compounds with their solvents. Such compounds with definite proportions between solutes and solvents are termed solvates. If the solvent is water, the compounds formed are termed hydrates. 

Ans. (a) 88.8%. (/>) The law of definite proportions states that all water, no matter what its source, contains the same percentage of its constituent elements. 

Does hydrogen peroxide, H202, have the same composition as water, H20 Does your answer violate the law of definite proportions Explain briefly. 

Ans. The compounds have different ratios of hydrogen to oxygen atoms, and thus different mass ratios. The law of definite proportions applies to each compound individually, not to the two different compounds. H20 and H202 each follow the law of definite proportions (and together they also follow the law of multiple proportions). 

This equation is valid for all species Ah a fact that is a consequence of the law of definite proportions. The molar extent of reaction is a time-dependent extensive variable that is measured in moles. It is a useful measure of the progress of the reaction because it is not tied to any particular species A. Changes in the mole numbers of two species j and k can be related to one another by eliminating between two expressions that may be derived from equation 1.1.4. 

Berzelius, J. (1814, 1815). Experiments to determine the definite proportions in which the elements of organic nature are combined. Annals of Philosophy 4 409-510, 5 93-101, 174-184, 260-275. 

In Josiah P. Cooke s projected three-volume course on chemical philosophy at Harvard University, the first volume treated chemical physics, the second was to cover electricity, and the third was to deal with stoiochiometry and the principles of chemical classification.60 Similarly, in Wurtz s Introduction a Vetude de la chimie (1885), it was not until page 206 that Wurtz began discussing the law of definite proportions, following a long section on the physical properties of bodies. 61... 

Thomas Thomson, "On the Daltonian Theory of Definite Proportions in Chemical Combinations," Annals of Philosophy 2 (1813) 3243, on 4142. 

On the other hand, a very large number of two-component crystals are known in which the components are present in definite proportions, and whose structures are different from those of the separate materials in their crystals. These are the complexes, or compounds in the Phase Rule sense. 

In your notebook, list the main ideas in Dalton s atomic theory. Explain how this theory enabled chemists to explain the three mass laws the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. 

Mixtures (or formulations) consist of two or more components combined in definite proportions such that the sum of their fractions is unity [Claringbold (1955)]. The mathematical expression of this concept is... 

At the time of his sixty-eighth birthday, Gahn received a novel congratulatory note from Berzelius, which read "From Herr Assessor s last letter I was happy to find new support for the doctrine of definite proportions. Heir Assessor was 68 on August 19 the following day (the 20th) I became 34 now 34X2=68, from whence it follows that Herr Assessor is equal to a multiple of me by two. .." (56). 

Dalton s Law of Multiple Proportions meant that two elements combine in simple whole number ratios. Dalton believed that compounds found in nature would be simple combinations. Hence, knowing that hydrogen combines with oxygen to give water, Dalton s formula for water would consist of 1 H and 1 O. Its formula would be HO using modern nomenclature. Both Proust s Law of Definite Proportions and Dalton s Law of Multiple Proportions are outcomes of an atomic view of nature. In 1808 Dalton published his table of relative atomic weights along with his ideas on atomism in A New System of Chemical Philosophy. 

Lattice Points positions in a unit cell occupied by atom, molecules, or ions Law of Definite Proportion law that states that different samples of the same compound always contain elemental mass percentages that are constant Law of Mass Action mathematical expression based on the ratio between products and reactants at equilibrium, an equation to determine the equilibrium rate constant Law of Multiple Proportions law that states when two elements combine to form more than one compound that the mass of one element compared to the fixed mass of... 

But, if atoms were little balls that always united in the same simple ratios to make compound particles , this explained why chemical reactions between elements always took place in constant and simple proportions. It was why, for example, a certain mass of mercury always combined, during calcination, with another fixed mass of oxygen. French chemist Louis Joseph Proust enshrined this principle in his Law of Definite Proportions in 1788. Not that... 

The trend was definitely toward the principle of fixed composition, but the empirical evidence in its support was still unreliable and allowed room for the doubts of the honest sceptic. Credit is usually given to Joseph-Louis Proust for bringing the law of definite proportions into the continuing consciousness of the chemical community. Proust thought his data justified the assumption of fixed composition and took it as a firm operating principle, very much as Lavoisier had assumed the conservation principle as an axiom. For example, Proust claimed that the quantity of copper oxide prepared from copper carbonate was always the same whatever process used, and that every chemical entity was characterized by a fixed composition. 

Berthollet s theory actually challenged Proust s basic rule of definite proportion, which was the cause of the debate, but the empirical evidence of both sides was inadequate to resolve the dispute. The controversy was more important by what it suggested than by what it accomplished. Henceforth, it became imperative to seek a clear understanding of the causes underlying the apparent fact of constant proportions. ... 

Most chemists at that time would hardly have found Berthollets view of variable composition a welcome idea, but even the acceptable (and empirically derived) chemical rules, such as definite proportions, needed a rational justification. Daltons atomic theory in 1808, like that of Berthollet, came from outside the mainstream of the empirical chemical story that this account has been following, but it produced so functional a rationale for the explicit laws of chemical composition, that the whole dispute regarding definite or indefinite composition became moot. 

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