Element-compound combination reactions

Objective 7 In combination reactions, two or more elements or compounds combine to form one compound. Combination reactions are also called synthesis reactions. The following are examples of combination reactions. 

In particular, one can combine reactions to yield the aG. , AH and ASj for fonnation of compounds from their elements, quantities rarely measurable directly. (Many AH s.for fonnation of substances are easily... 

Oxidation Combining elemental compounds with oxygen to form a new compound. A part of the metabolic reaction. 

A combination reaction is a reaction of two reactants to produce one product. The simplest combination reactions are the reactions of two elements to form a compound. After all, if two elements are treated with each other, they can either react or not. There is no other possibility, since neither can decompose. In most reactions like this, there will be a reaction. The main problem is to write the formula of the one product correctly, and then balance the equation. In this process, first determine the formulas of the products from the rules of chemical combination (Chap. 5). Only when the formulas of the reactants and products have all been written down do you balance the equation by adjusting the coefficients. 

There are a number of interferences that can occur in atomic absorption and other flame spectroscopic methods. Anything that decreases the number of neutral atoms in the flame will decrease the absorption signal. Chemical interference is the most commonly encountered example of depression of the absorption signal. Here, the element of interest reacts with an anion in solution or with a gas in the flame to produce a stable compound in the flame. For example, calcium, in the presence of phosphate, will form the stable pyrophosphate molecule. Refractory elements will combine with 0 or OH radicals in the flame to produce stable monoxides and hydroxides. Fortunately, most of these chemical interferences can be avoided by adding an appropriate reagent or by using a hotter flame. The phosphate interferences, for example, can be eliminated by adding 1 % strontium chloride or lanthanum chloride to the solution. The strontium or lanthanum preferentially combines with the phosphate to prevent its reaction with the calcium. Or, EDTA can be added to complex the calcium and prevent its combination with the phosphate. 

The science of the elements and compounds can be construed as the branch of chemistry that describes the composition and properties (both chemical and physical, e.g., melting points) of all of the known elements and compounds. The reactions they undergo describes how elements combine... 

Combination reactions are reactions in which two or more reactants (elements or compounds) combine to form one product. Although these reactions may be of a number of different types, some types are definitely redox reactions. These include reactions of metals... 

Combination reactions are usually redox reactions in which two or more reactants (elements or compounds) combine to form one product. 

Cadmium(II) bromide Cd + 2Br " —> CdBr. This compound is used in photography, engraving, and lithography. The other halogen elements also combine with cadmium in a similar ionic reaction as with bromine. 

Perhaps it is worth emphasizing again that the importance of Dalton s theory didn t lie in the assumption that matter is composed of indestructible atoms. That was a very old idea. On the contrary, his idea was significant because it was a theory that explained how chemical compounds are formed and because the idea of atoms with different relative weights made it possible to turn chemistry into a quantitative science. As long as chemists held on to the old idea that elements could combine with one another in a variety of different proportions, they could describe chemical reactions only in a qualitative manner. It was Dalton who changed all this. 

Elements are fundamental substances that cannot be broken down into smaller chemical components. The smallest unit of an element is an atom, a term based on the Greek word atomos, meaning indivisible. But atoms are divisible—they consist of a nucleus containing positively charged particles called protons and electrically neutral particles called neutrons, surrounded by a swarm of electrically negative particles called electrons. In chemical reactions, atoms interact and combine to form a molecule of a compound. (Chemical reactions also occur when the atoms in molecules interact and combine to form even bigger com-... 

The combining of elements to form compounds (like NaCl) is a particularly common kind of combination reaction. Here s another example ... 

The atoms of various elements can combine to form new substances. For example, atoms of the elements hydrogen and oxygen combine to form water. This chemical combination of atoms of two elements to form a new product is an example of a chemical reaction. Note that the properties of water, a colorless, tasteless liquid, are very different from those of its constituent elements, which are both gases. A substance, such as water, made from the chemical combination of atoms of two or more elements is called a compound. Whde an element cannot be broken down into a simpler form by normal chemical means, a compound can be broken down into atoms of... 

Chemistry involves the transformation of matter. These transformations largely involve substances that are compounds. Elements combine to form compounds in combination reactions, whereas decomposition reactions result in a chemical compound being broken into smaller compounds and/or elements. Still other reactions involve the exchange of atoms between compounds, resulting in new compounds. The number of identified chemical compounds is approximately 10 million and increasing by several hundred thousand each year. 

Although sulphur in the compact form appears to be a comparatively inactive clement, yet when in a fine state of division it reacts with many metals, and at elevated temperatures it combines directly with nearly all other elements (exceptions being nitrogen, iodine, beryllium, gold, platinum and iridium) to form stable binary compounds, the reactions often occurring with great vigour. 

Combination reactions. Elements and/or compounds combine into one product. 

Yb-ln-Sb. The ternary YbsI Sbe compound was obtained from a direct element combination reaction in a sealed graphite tube at 973 K, and its crystal structure was determined by X-ray single crystal diffraction methods. It crystallizes in the Ba5ln2Sb6 structure type with a unit cell of a = 0.73992, b = 2.3001, c = 0.45139 (Kim et al., 2000). 

Two elements reacting to form a compound is a combination reaction. This process may be described by the general formula ... 

Fluorine is an extremely reactive element, which combines directly or indirectly with nearly all substances. Reactions with elementar fluorine are very violent and sometimes explosions occur so that extreme care must be taken. As the deposition potential of fluorine greatly exceeds the deposition potentials of all other substances, it can be only prepared by electrolysis of its compounds. Due to the fact that water is decomposed by fluorine electrolysis must be effected in an anhydrous medium. Since the days of Moissan who first succeeded in isolating free fluorine, anhydrous hydrofluoric acid is used to prepare it. The electrical conductivity of this substance is very small and must be increased by the addition of alkali fluorides. 

In combination reactions, the reactants combine to form a single product. Because a combination of an element and a compound or two compounds would be difficult to classify as a combination reaction, the reactions on the AP test that are combination reactions tend to use two elements. So, if you encounter two elements on the test, they will undergo a combination reaction. 

John Dalton examined the masses of compounds before and after a reaction. Dalton s research led him to propose the law of multiple proportions The masses of the elements that combine can be expressed in small whole number ratios. 

Nitrogen forms binary compounds with most other elements, although many of them are not obtained by direct combination reactions. The ionic compounds (e.g., Mg3N2 or Na3N) result when the difference between the electronegativities of the two atoms is about 1.6 units or... 

Combination reactions involve the reaction of two (or more) snbstances to form one compound. Perhaps the easiest combination reaction to recognize is one in which two free elements (at least one of which is a nonmetal) react with each other. The elements can do httle except react with each other (or not react at all). For example, if we treat aluminum metal with chlorine gas, the elements can combine to form aluminum chloride ... 

In another type of combination reaction, a compound may be able to combine with a particular free element to form another compound as the only product. This occurs most often when the free element is the same as one of the elements in the original compound. An example of such a combination reaction is... 

In yet another type of combination reaction, two compounds containing the same element may be able to combine to form a single, more complex compound. The element the reactants have in common is very often oxygen ... 

Decomposition reactions have the opposite effect from combination reactions. In a decomposition reaction, a single compound can decompose to two elements, to an element and a simpler compound, to two simpler compounds, or (rarely) to another combination of products. Ternary componnds, compounds containing three elements, do not decompose into three uncombined elements. Decomposition reactions are easy to identify because there is only one reactant. Table 8.1 summarizes the most common types of decomposition reactions. 

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