Writing Balanced Equations for Combination and Decomposition Reactions Write a balanced equation for (a) the combination reaction between lithium metal and fluorine gas and (b) the decomposition reaction that occurs when solid barium carbonate is heated (two products form, a solid and a gas). Write a balanced equation for (a) solid mercury (II) sulfide decomposing into its component elements when heated and (b) aluminum metal combining with oxygen in the air.
Answer : Step 1 A combination reaction (also known as a synthesis reaction) is a reaction where two or more elements or compounds (reactants) combine to form a single compound (product). Such reactions may be represented by equations of the following form: X + Y XY. Combination reactions can involve different types of reactants: Type Example a) Between elements C + O CO Carbon completely burnt in oxygen 2 2 yields carbon dioxide b) Between CaO + H2 Calcium oxide (lime) combined with compounds Ca(OH) water gives calcium hydroxide (slaked 2 lime) c) Between elements 2CO + O 2CO2 2 Oxygen combines with carbon and compounds monoxide, and carbon dioxide is formed. There is no specific number of reactants in a combination reaction. Step 2 (a)The symbol for lithium is Li. With the exception of mercury, all metals are solids at room temperature. Fluorine occurs as a diatomic molecule. Thu s, the reactants are Li ) and F2(g)The product will consist of a metal and a nonmetal, so we expect it to be an ionic solid. Lithium ions have a +1 charge, Li+ whereas fluoride ions have a -1 charge, F- Thus, the chemical formula for the product is LiF. The balanced chemical equation is 2Li(s)+F2(g)2LiF(s). Step 3 (b) The chemical formula for barium carbonate is BaCO3.As noted in the text, many metal carbonates decompose to form metal oxides and carbon dioxide when heated. In Equation 3.7, for example, CaCO3 decomposes to form CaO and CO2 .Thus, we would expect that BaCO3 decomposes to form BaO and CO2 .Barium and calcium are both in group 2A in the periodic table, moreover, which further suggests they would react in the same way: BaCO3(s)BaO(s)+CO2(g).