Conservation of atoms

Belief in the conservation of atoms is based upon a generalization that has stood the test of many... 

Since the mass of a mole of water is the sum of the masses of the atoms in the mole of water, the conservation of mass implies conservation of atoms. 

All equations are based upon the conservation of atoms. Every symbol, when multiplied by the subscript after it and the coefficient before the formula, must appear as often on the left side of the equation as on the right. 

Condensation polymerization, 346 Conservation of atoms, 40 of charge, 80, 218 of mass, 40... 

A chemical equation describes a chemical reaction in many ways as an empirical formula describes a chemical compound. The equation describes not only which substances react, but the relative number of moles of each undergoing reaction and the relative number of moles of each product formed. Note especially that it is the mole ratios in which the substances react, not how much is present, that the equation describes. In order to show the quantitative relationships, the equation must be balanced. That is, it must have the same number of atoms of each element used up and produced (except for special equations that describe nuclear reactions). The law of conservation of mass is thus obeyed, and also the "law of conservation of atoms. Coefficients are used before the formulas for elements and compounds to tell how many formula units of that substance are involved in the reaction. A coefficient does not imply any chemical bonding between units of the substance it is placed before. The number of atoms involved in each formula unit is multiplied by the coefficient to get the total number of atoms of each element involved. Later, when equations with individual ions are written (Chap. 9), the net charge on each side of the equation, as well as the numbers of atoms of each element, must be the same to have a balanced equation. The absence of a coefficient in a balanced equation implies a coefficient of 1. 

Alternatively, the conservation of atomic species is commonly expressed in the form of chemical equations, corresponding to chemical reactions. We refer to the stoichiometric constraints expressed this way as chemical reaction stoichiometry. A simple system is represented by one chemical equation, and a complex system by a set of chemical equations. Determining the number and a proper set of chemical equations for a specified list of species (reactants and products) is the role of chemical reaction stoichiometry. 

The chemical equation then represents a conservation of atoms, which ensures conservation of mass and an alternative view of the species as molecules or moles. The stoichiometric coefficients correspond to the number of molecules or moles of each species. 

III. If Nf is the number of gram-atoms of component element i and n is the number of moles of species j, then the conservation of atom types requires that... 

The mass balance is a statement of the conservation of matter. It really refers to conservation of atoms, not to mass. 

Students will write balanced chemical equations for the chemical changes observed and explain that an equation is balanced to reflect the conservation of atoms in a chemical change, as required in the law of conservation of matter. 

If, at 0 K, entropies of compounds are the sum of nonzero values assigned to each atom, conservation of atoms would ensure that the entropy change for all chemical reactions would be zero. This way of satisfying the third law would not be in agreement with the microscopic interpretation of entropy given in Chapter 5. 

Following the second approach, only the knowledge of the chemical species involved in the chemistry is sufficient. The problem can be formulated as follows given a list of chemical species S find a proper set of independent chemical equations R that ensures the conservation of atomic species N in terms of the molecular formulas of the system species. A proper set allows that any other chemical equation can be obtained from this by algebraic operations. A chemical species is characterized by formula, isomeric form and phase, and it may be neutral molecules, ionics and radicals. The atomic species can be atoms and charge (+ or -). 

Chemistry imposes a stricter constraint than simply conservation of mass Individual atoms must also be preserved. Let K =, 2,.. ., / be the atomic species present in any one of the components in the system. Let puc be the grams of atom K per gram of species / the matrix p,fc will be compactly indicated as p. Conservation of atoms can be expressed as... 

It is a very good practice to check every chemical equation that you write, to be sure that it agrees with the law of the conservation of atoms of every element. ... 

Note that there is ccniser ation of electric charge as well as conservation of atoms in ead. of these equations. 

Oxygen and hydrogen occur here on the left side and not oh the right side of the equation conservation of atoms is satisfied if SHgO is written in as the other products ... 

You must determine the unknown product of the reaction, X. This can be done through the conservation of atomic number and mass number. The periodic table can then be used to identify X. 

Notice that there is a conservation of atoms from the left to the right side of the equation. In other words, there is the same number of oxygen, hydrogen, and carbon atoms on the right as on the left. This means the equation is balanced. On the MCAT, if the answer is given in equation form, the correct answer will be a balanced equation unless specifically indicated to the contrary. 

Remember that atoms don t change in a chemical reaction they just rearrange. The number and kinds of atoms present in the reactants of a chemical reaction are the same as those present in the products. When stated this way, it becomes the law of conservation of atoms. For a chemical equation to accurately represent a reaction, the same number of each kind of atom must be on the left side of the arrow as are on the right side. If an equation follows the law of conservation of atoms, it is said to be balanced. 

Do both sides of the equation have the same number of each type of atom No. One carbon atom is on each side of the arrow, but the sodium, oxygen, and hydrogen atoms are not balanced. The equation, as written, does not truly represent the reaction because it does not show conservation of atoms. 

In reactions with intermediates, the constraints are usually best formulated in terms of conservation of atoms or groups. Hydroformylation, examined in examples in several later chapters, can illustrate this. The reaction is... 

The total number of nuclear charges in the products and in the reactants must be the same (conservation of atomic number). 

Note that the enthalpies of the reference state atomic species cancel by the conservation of atomic species, this will always occur. Thus, we have, as general results,... 

Pick s first law relates flux to concentration gradient at a given place and time, but it does not explicitly describe how the concentration at a point evolves with time. To obtain a complete description of the process as a function of both position and time, it is necessary to combine Equation (105) with the equation that describes the conservation of atoms of type i... 

Several approaches are suggested for the deduction of information on the causal chemical connectivity of the species, on the elementary reactions among the species, and on the sequence of the elementary reactions that constitute the reaction pathway and the reaction mechanism. Chemical reactions occur by the collisions of molecules, and such an event is called an elementary reaction for specified reactant and product molecules. A balanced stoichiometric equation for an elementary reaction yields the number of each type of molecule according to conservation of atoms, mass, and charge. Figure 1.1 shows a relatively simple reaction mechanism for the decomposition of ozone by light, postulated to occur in a series of three elementary steps. (The details of collisions of molecules and bond rearrangements are not discussed.) All approaches are based on the measurements of the concentrations of chemical species in the whole reaction system, not on parts, as has been the practice. 

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