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98 Chapter Three Stoichiometry Notice that now we have the same number of each type of atom represented among the reactants and the products. We can represent the preceding situation in a shorthand manner by the following chemical equation: CH 4 + 20 2 ~ CO 2 + 2H 2 0 We can check that the equation is balanced by comparing the number of each type of atom on both sides: CH 4 + 20 2 ~ CO 2 + 2H z O 7't t tt tt IC4H I ICI4HI 40 20 20 To summarize, we have Reactants Products 1 C 4H 40 1 C 4H 40 The Meaning of a Chemical Equation The chemical equation for a reaction gives two important types of information: the nature of the reactants and products and the relative numbers of each. The reactants and products in a specific reaction must be identified by experiment. Besides specifying the compounds involved in the reaction, the equation often gives the physical states of the reactants and products: State Symbol Solid Liquid Gas Dissolved in water (in aqueous solution) (s) (I) (g) (aq) For example, when hydrochloric acid in aqueous solution is added to solid sodium hydro- gen carbonate, the products carbon dioxide gas, liquid water, and sodium chloride
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Unformatted text preview: (which dissolves in the water) are formed: HCI(aq) + NaHC0 3 (s) ~ CO 2 (g) + H 2 0(l) + NaCl(aq) The relative numbers of reactants and products in a reaction are indicated by the co-efficients in the balanced equation. (The coefficients can be determined because we know that the same number of each type of atom must occur on both sides of the equation.) For example, the balanced equation CH 4 (g) + 20 2 (g) ~ CO 2 (g) + 2H z O(g) can be interpreted in several equivalent ways, as shown in Table 3.2. Note that the total mass is 80 grams for both reactants and products. We expect the mass to remain constant, since chemical reactions involve only a rearrangement of atoms. Atoms, and therefore mass, are conserved in a chemical reaction. From this discussion you can see that a balanced chemical equation gives you a great deal of information....
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This note was uploaded on 12/13/2010 for the course CHEM 2301 taught by Professor Bill during the Spring '10 term at South Texas College.

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