Matter pure substances

The term "pliase" for a pure substance indicates a state of matter - that is, solid, liquid, or gas. For mi. tures, however, a more stringent connotation must be used, since a totally liquid or solid system may contain more dian one phase. A phase is characterized by uniformity or homogeneity die same composition and properties must c. ist tliroughout the pliase region. At most temperatures and pressures, a pure substance normally exists as a single phase. At certain temperatures mid pressures, two or perhaps even dmee phases can coe.xist in equilibrium. 

An element is a type of matter that cannot be broken down into two or more pure substances. There are 115 known elements, of which 91 occur naturally. 

It is impossible to have liquid carbon dioxide at temperatures above 31°C, no matter how much pressure is applied. Even at pressures as high as 1000 atm, carbon dioxide gas does not liquefy at 35 or 40°C. This behavior is typical of all substances. There is a temperature, called the critical temperature, above which the liquid phase of a pure substance cannot exist The pressure that must be applied to cause condensation at that temperature is called the critical pressure. Quite simply, the critical pressure is the vapor pressure of the liquid at the critical temperature. 

FIGURE G.5 The hierarchy of materials matter consists of either mixtures or substances substances consist of either compounds or elements. Physical techniques are used to separate mixtures into pure substances. Chemical techniques are used to separate compounds into elements. 

In the method of classification of matter based on composition, a given specimen of material is regarded as either a pure substance or a mixture. An outline of this classification scheme is shown in Table 1-2. The term pure substance (or merely substance) refers to a material all parts of which have the same composition and which has a definite and unique set of properties. In contrast, a mixture consists of two or more substances and has a somewhat arbitrary composition. The properties of a mixture are not unique, but depend on its composition. The properties of a mixture tend to reflect the properties of the substances of which it is composed that is, if the composition is changed a little, the properties will change a little. 

The notion of standard enthalpy of formation of pure substances (AfH°) as well as the use of these quantities to evaluate reaction enthalpies are covered in general physical chemistry courses [1]. Nevertheless, for sake of clarity, let us review this matter by using the example under discussion. The standard enthalpies of formation of C2H5OH(l), CH3COOH(l), and H20(1) at 298.15 K are, by definition, the enthalpies of reactions 2.3,2.4, and 2.5, respectively, where all reactants and products are in their standard states at 298.15 K and the elements are in their most stable physical states at that conventional temperature—the so-called reference states at 298.15 K. 

Although the change in state of the heat bath, hence the value of Q, usually is determined by measuring a change in temperature, this is a matter of convenience and custom. For a pure substance the state of a system is determined by specifying the values of two intensive variables. For a heat bath whose volume (and density) is hxed, the temperature is a convenient second variable. A measurement of the pressure, viscosity, or surface tension would determine the state of the system equally as well. This point is important to the logic of our development because a later dehnition of a temperature scale is based on heat measurements. To avoid circularity, the measurement of heat must be independent of the measurement of temperature. 

Elements and compounds constitute the world of pure substances. An element is a substance that cannot be decomposed by any chemical reaction into simpler substances. Elements are composed of only one type of atom and all atoms of a given type have the same properties. Pure substances cannot be separated into other kinds of matter by any physical process. We are familiar with many pure substances water, iron, mercury, iodine, helium, rust, diamond, table salt, sugar, gypsum, and so forth. Among the pure substances listed above, iron, mercury, iodine, diamond (pure carbon), and helium are elements. We are also familiar with mixtures of pure substances. These include the air that we breathe, milk, molasses, beer, blood, coffee, concrete, egg whites, ice cream, dirt, steel, and so on. 

Finally, let s back up to the definition of chemistry as a science having to do with matter, as stated above. So what are we talking about here Matter is anything that has mass and occupies space. That includes everything that can be perceived by our human senses and a lot of stuff that cannot be. Matter includes, but is not limited to, the elements and compounds (pure substances) and mixtures of pure substances. 

A phase is defined as a state of matter that is uniform throughout in terms of its chemical composition and physical state in other words, a phase may be considered a pure substance or a mixture of pure substances wherein intensive properties do not vary with position. Accordingly, a gaseous mixture is a single phase, and a mixture of completely miscible liquids yields a single hquid phase in contrast, a mixture of several solids remains as a system with multiple solid phases. A phase rule therefore states that, if a limited number of macroscopic properties is known, it is possible to predict additional properties. 

A substance can be classified chemically in many ways. One of the simplest ways to classify a substance is as an element or a compound. An element is a pure substance that cannot be changed into a simpler substance by chemical means. Elements are the building blocks of nature all matter is composed of elements. The periodic table is a concise map that organizes chemical elements into columns (groups) and rows (periods) based on their chemical properties. Currently, there are 118 known chemical elements, with whole numbers 1 to 118. These numbers are referred to as the element s atomic number and give the number of protons in the nucleus of an atom of the element. For example, carbon s atomic number is 6 and each carbon atom has 6 protons in its nucleus. The first 92 elements occur naturally, and those above atomic number 92 are synthesized through nuclear reactions using particle accelerators. Element 118 was just confirmed in the fall of 2006, and by now, more elements may have been produced. 

Avogadro s Law. Equal volumes of different gases at the same pressure and temperature contain the same number of molecules. From ihe concept of Ihe mole, a pound-mole of any subslance contains a mass equal in pounds to the molecular weight of the subslance, Thus the ratio of mole weigh lo molecular weight is a constant, and a mole or a chemically pure substance contains ihe same number of molecules, no matter what the subslance may be. Since a mole of any ideal gas occupies the same volume at a given pressure and temperature (ideal gas law), il follows that equal volumes of different gases at the same pressure and temperature contain the same number of molecules. 

Although only 90 elements occur naturally, there are obviously far more than 90 different kinds of matter on earth. Just look around, and you ll surely find a few hundred. All the many kinds of matter can be classified as either pure substances or mixtures, as shown in Figure 2.7. Pure substances, in turn, can be either elements... 

Anyhow, at 25 °C, an ideal gas at 1 atm is 0.041 M. Condensed matter with small molecules (or metals such as silver and gold) can be up to 100 M. Hence, at their boiling points, most substances show an activity coefficient in the gaseous state (comparing with the molarity of the condensed matter and not the conventional activity a = 1 of pure substances) of the order of magnitude 1000. In view of the almost ideal nature of the gaseous state, it would perhaps be more appropriate to say that the condensed matter has/ 10 3 relative to the vapour at 1 atm. 

By the same token, it originally demanded an enormous experimental effort to purify water by distillation and keep it free from contaminants such as C02 in order to prove that the pure substance indeed contains 10 7 M Haq and 10-7 M OH" in equilibrium. After S. P. L. Sprensen introduced the concept pH, it became plausible to determine pH by electrode potentials, first from the classical hydrogen electrode with finely divided platinum catalyst (the conditions for the standard oxidation potential E° to show its zero point is a monument for the difficulties when mixing thermodynamical prescriptions for gaseous and condensed matter ... 

A solution is a homogeneous mixture of a solute and solvent. In a classification of matter, matter is divided into mixtures and pure substances. Mixtures are divided into homogenous mixtures, solutions, and heterogeneous mixtures such as suspensions. Pure substances are divided into elements made up of atoms and compounds made up of molecules. 

Define mixtures, pure substances, heterogeneous and homogeneous matter, elements, and compounds. 

Matter can be either a pure substance or a mixture. Pure substances cannot be further broken down into simpler components through physical processes and can be either elements (one type of atom) or compounds (more than one type of atom). Mixtures can be homogeneous (aka. solutions) or heterogeneous. Heterogeneous mixtures exhibit phase boundaries, or sharp demarcations where the chemical and/or physical properties of the sample change. Mixtures are separable into pure substances through physical processes. 

An atom is the fundamental building block of all matter. Molecules are aggregates of atoms chemically bonded into a discrete unit. Compounds are comprised of two or more kinds of atoms. Mixtures are aggregates of two or more pure substances that can be separated through physical means. 

The word "matter" describes everything that has physical existence, i.e. has mass and takes up space. However, the make up of matter allows it to be separated into categories. The two main classes of matter are pure substance and mixture. Each of these classes can also be divided into smaller categories such as element, compound, homogeneous mixture or heterogeneous mixture based on composition. 

PURE SUBSTANCES A pure substance is a form of matter with a definite composition and distinct properties. This type of matter can not be separated by ordinary processes like filtering, centrifuging, boiling or melting. 

Up to now the applications we have considered have involved one component systems involving only pure substances and representing a fixed amount of matter (usually 1 mole). 

Contrast this availability in the inorganic realm with the substances that are readily available from organic nature. How could chemists extract pure substances from samples of plant tissue or flesh If plant or animal matter is subjected to distillation, then, typically, a black residue remains in the distillation vessel, and liquid and gaseous substances are driven off. The distillation of different plant substances produces substances that are qualitatively similar, so... 

All matter can be classified into two groups mixtures and pure substances. A mixture is a physical combination of two or more kinds of matter. For example, soil is a mixture of sand, clay, silt, and decomposed leaves and animal bodies. If you look at soil under a magnifying glass, you can see these different components. Figure 1.11 shows another way to see the components of soil. 

Pure substances are those which do not contain any organic or inorganic matter. 

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