Compound A substance with constant

Compound a substance with constant composition that can be broken down into elements by chemical processes. Concentration cell a galvanic cell in which both compartments contain the same components, but at different concentrations. (11.4)... 

Pure substance a substance with constant composition a pure element or a pure compound. 

A compound is an electrically neutral substance that consists of two or more different elements with their atoms present in a definite ratio. Water, for instance, is a compound of hydrogen and oxygen, with two hydrogen atoms for each oxygen atom. Whatever the source of the water, it has exactly the same composition indeed, a substance with a different ratio of atoms would not be water Chemists took a big step forward when they first noticed this invariance of composition, for it suggested an underlying order in nature. They summarized the observation as the law of constant composition. The law was important historically, because it suggested to chemists that compounds consisted of specific combinations of atoms. 

They varied only the values of the adsorption and desorption rate constants of the reaction intermediate B, and by using the simplest Langmuir kinetics, they calculated time-concentration curves of compounds A, B, and C shown in Fig. 5. Also from this example, which does not consider any step as clearly rate determining, it is evident how very different concentration versus time plots can be obtained for the same sequence of surface reactions if adsorption and desorption of the intermediate B proceed by different rates, which are, however, comparable with the rate of surface reactions. In particular, the curves in the first and second columns of Fig. 5 simulate the parallel formation of substances B and C, at least... 

At high F, when the spacing of vibrational energy levels is low with respect to thermal energy, crystalline solids begin to show the classical behavior predicted by kinetic theory, and the heat capacity of the substance at constant volume (Cy) approaches the theoretical limit imposed by free motion of all atoms along three directions, in a compound with n moles of atoms per formula unit limit of Dulong and Petit) ... 

The search for chemical compounds that will cure disease, alleviate pain, or otherwise extend human life and make it more comfortable and pleasurable has been a part of human culture as far back as we know. Those who practice forms of traditional medicine have, over the centuries, developed extensive and sophisticated pharmacopoeias that contain many such compounds extracted from plants, animals, and minerals in their surrounding environments. Modern medical researchers have developed their own treasure chests of drugs, many of which have been derived from traditional medicines, and many others of which have been synthesized from basic materials, often by way of complex chemical reactions. Even after thousands of years of drug research, however, healers are not completely satisfied with the armory of chemicals available for their use. People are constantly searching for new compounds that will act more efficiently and more safely than existing pharmaceuticals and for substances with which to combat new forms of disease. 

B. Slush Baths. Liquid nitrogen and Dry Ice are convenient and inexpensive refrigerants. But, as shown in the examples in this chapter, a wider range of low-temperature baths is necessary for trap-to-trap fractionation of gases and for the characterization of a substance by vapor pressure measurements. A convenient constant-temperature slush bath consists of a mixture of a frozen compound in equilibrium with its liquid. The bath is made in a clean Dewar no more than... 

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