{"id":125,"date":"2017-12-14T21:26:45","date_gmt":"2017-12-14T21:26:45","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/chapter\/composition-decomposition-and-combustion-reactions\/"},"modified":"2017-12-14T21:26:45","modified_gmt":"2017-12-14T21:26:45","slug":"composition-decomposition-and-combustion-reactions","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-introductory-chemistry\/chapter\/composition-decomposition-and-combustion-reactions\/","title":{"raw":"Composition, Decomposition, and Combustion Reactions","rendered":"Composition, Decomposition, and Combustion Reactions"},"content":{"raw":"
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Learning Objectives<\/h3>\n
  1. Recognize composition, decomposition, and combustion reactions.<\/li>\n\t
  2. Predict the products of a combustion reaction.<\/li>\n<\/ol><\/div>\n<\/div>\n

    Three classifications of chemical reactions will be reviewed in this section. Predicting the products in some of them may be difficult, but the reactions are still easy to recognize.<\/p>\n

    A composition reaction<\/a><\/span>\u00a0(sometimes also called a combination reaction<\/em> or a synthesis reaction<\/em>) produces a single substance from multiple reactants. A single substance as a product is the key characteristic of the composition reaction. There may be a coefficient other than one for the substance, but if the reaction has only a single substance as a product, it can be called a composition reaction. In the reaction<\/p>\n2 H2<\/sub>(g) +\u00a0O2<\/sub>(g) \u2192\u00a02 H2<\/sub>O(\u2113)<\/span><\/span>\n

    water is produced from hydrogen and oxygen. Although there are two molecules of water being produced, there is only one substance\u2014water\u2014as a product. So this is a composition reaction.<\/p>\n

    A decomposition reaction<\/a><\/span>\u00a0starts from a single substance and produces more than one substance; that is, it decomposes. One substance as a reactant and more than one substance as the products is the key characteristic of a decomposition reaction. For example, in the decomposition of sodium hydrogen carbonate (also known as sodium bicarbonate),<\/p>\n2 NaHCO3<\/sub>(s) \u2192\u00a0Na2<\/sub>CO3<\/sub>(s) +\u00a0CO2<\/sub>(g) +\u00a0H2<\/sub>O(\u2113)<\/span><\/span>\n

    sodium carbonate, carbon dioxide, and water are produced from the single substance sodium hydrogen carbonate.<\/p>\n

    Composition and decomposition reactions are difficult to predict; however, they should be easy to recognize.<\/p>\n\n

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    Example 9<\/h3>\n

    Identify each equation as a composition reaction, a decomposition reaction, or neither.<\/p>\n\n

    1. Fe2<\/sub>O3<\/sub> +\u00a03 SO3<\/sub> \u2192\u00a0Fe2<\/sub>(SO4<\/sub>)3<\/sub><\/li>\n\t
    2. NaCl +\u00a0AgNO3<\/sub> \u2192\u00a0AgCl +\u00a0NaNO3<\/sub><\/li>\n\t
    3. (NH4<\/sub>)2<\/sub>Cr2<\/sub>O7<\/sub> \u2192\u00a0Cr2<\/sub>O3<\/sub> +\u00a04 H2<\/sub>O +\u00a0N2<\/sub><\/li>\n<\/ol>

      Solution<\/p>\n\n

      1. In this equation, two substances combine to make a single substance. This is a composition reaction.<\/li>\n\t
      2. Two different substances react to make two new substances. This does not fit the definition of either a composition reaction or a decomposition reaction, so it is neither. In fact, you may recognize this as a double-replacement reaction.<\/li>\n\t
      3. A single substance reacts to make multiple substances. This is a decomposition reaction.<\/li>\n<\/ol>

        Test Yourself<\/em><\/p>\n

        Identify the equation as a composition reaction, a decomposition reaction, or neither.<\/p>\nC3<\/sub>H8<\/sub> \u2192\u00a0C3<\/sub>H4<\/sub> +\u00a02 H2<\/sub><\/span><\/span>\n

        Answer<\/em><\/p>\n

        decomposition<\/p>\n\n<\/div>\n

        A combustion reaction<\/a><\/span>\u00a0occurs when a reactant combines with oxygen, many times from the atmosphere, to produce oxides of all other elements as products; any nitrogen in the reactant is converted to elemental nitrogen, N2<\/sub>. Many reactants, called fuels<\/em>, contain mostly carbon and hydrogen atoms, reacting with oxygen to produce CO2<\/sub> and H2<\/sub>O. For example, the balanced chemical equation for the combustion of methane, CH4<\/sub>, is as follows:<\/p>\nCH4<\/sub> +\u00a02 O2<\/sub> \u2192\u00a0CO2<\/sub> +\u00a02 H2<\/sub>O<\/span><\/span>\n

        Kerosene can be approximated with the formula C12<\/sub>H26<\/sub>, and its combustion equation is<\/p>\n2 C12<\/sub>H26<\/sub> +\u00a037 O2<\/sub> \u2192\u00a024 CO2<\/sub> +\u00a026 H2<\/sub>O<\/span><\/span>\n

        Sometimes fuels contain oxygen atoms, which must be counted when balancing the chemical equation. One common fuel is ethanol, C2<\/sub>H5<\/sub>OH, whose combustion equation is<\/p>\nC2<\/sub>H5<\/sub>OH +\u00a03 O2<\/sub> \u2192\u00a02 CO2<\/sub> +\u00a03 H2<\/sub>O<\/span><\/span>\n

        If nitrogen is present in the original fuel, it is converted to N2<\/sub>, not to a nitrogen-oxygen compound. Thus, for the combustion of the fuel dinitroethylene, whose formula is C2<\/sub>H2<\/sub>N2<\/sub>O4<\/sub>, we have<\/p>\n2 C2<\/sub>H2<\/sub>N2<\/sub>O4<\/sub> +\u00a0O2<\/sub> \u2192\u00a04 CO2<\/sub> +\u00a02 H2<\/sub>O +\u00a02 N2<\/sub><\/span><\/span>\n

        \n

        Example 10<\/h3>\n

        Complete and balance each combustion equation.<\/p>\n\n

        1. the combustion of propane, C3<\/sub>H8<\/sub><\/li>\n\t
        2. the combustion of ammonia, NH3<\/sub><\/li>\n<\/ol>

          Solution<\/p>\n\n

          1. \n

            The products of the reaction are CO2<\/sub> and H2<\/sub>O, so our unbalanced equation is<\/p>\nC3<\/sub>H8<\/sub> +\u00a0O2<\/sub> \u2192\u00a0CO2<\/sub> +\u00a0H2<\/sub>O<\/span><\/span>\n

            Balancing (and you may have to go back and forth a few times to balance this), we get<\/p>\nC3<\/sub>H8<\/sub> +\u00a05 O2<\/sub> \u2192\u00a03 CO2<\/sub> +\u00a04 H2<\/sub>O<\/span><\/span><\/li>\n\t

          2. \n

            The nitrogen atoms in ammonia will react to make N2<\/sub>, while the hydrogen atoms will react with O2<\/sub> to make H2<\/sub>O:<\/p>\nNH3<\/sub> +\u00a0O2<\/sub> \u2192\u00a0N2<\/sub> +\u00a0H2<\/sub>O<\/span><\/span>\n

            To balance this equation without fractions (which is the convention), we get<\/p>\n4 NH3<\/sub> +\u00a03 O2<\/sub> \u2192\u00a02 N2<\/sub> +\u00a06 H2<\/sub>O<\/span><\/span><\/li>\n<\/ol>

            Test Yourself<\/em><\/p>\n

            Complete and balance the combustion equation for cyclopropanol, C3<\/sub>H6<\/sub>O.<\/p>\n

            Answer<\/em><\/p>\n

            C3<\/sub>H6<\/sub>O +\u00a04 O2<\/sub> \u2192\u00a03 CO2<\/sub> +\u00a03 H2<\/sub>O<\/p>\n\n

            \n\n[caption id=\"attachment_3213\" align=\"alignnone\" width=\"400\"]\"Propane<\/a> Propane is a fuel used to provide heat for some homes. Propane is stored in large tanks like that shown here. Source: \u201cflowers and propane\u201d by vistavision is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic[\/caption]\n\n<\/div>\n<\/div>\n
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            Key Takeaways<\/h3>\n