{"id":383,"date":"2017-08-21T06:45:54","date_gmt":"2017-08-21T06:45:54","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/chemistry\/?page_id=383"},"modified":"2020-02-03T18:15:17","modified_gmt":"2020-02-03T18:15:17","slug":"classifying-chemical-reactions-and-predicting-products","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/chemistry\/classifying-chemical-reactions-and-predicting-products\/","title":{"rendered":"Classifying Chemical Reactions and Predicting Products"},"content":{"rendered":"<div class=\"twelve columns\" style=\"margin-top: 10%;\">\n<div class=\"advance\">\n<p><a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/reactions-and-reactivity\">Workshop Index<\/a>\u00a0<a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/types-of-chemical-equations\">Next Lesson\u00a0\u27a1<\/a><\/p>\n<\/div>\n<p><!-- UPDATE NEXT\/PREVIOUS ABOVE --><\/p>\n<p><!-- CONTENT STARTS HERE --><\/p>\n<h1 id=\"title\">Classifying Chemical Reactions and Predicting Products<\/h1>\n<h4>Objective<\/h4>\n<p>In this lesson, we will review different types of\u00a0chemical reactions and discuss how to predict the products of a\u00a0reaction based\u00a0upon the type of chemical reaction that will occur.<\/p>\n<section>\n<h3>Classifying Chemical Reactions<\/h3>\n<p>Chemical reactions occur\u00a0when substances combine or <abbr title=\"To break down into its original parts; decay\">decompose<\/abbr> forming new types of chemical substances with different <abbr title=\"A characteristic of a material\">properties<\/abbr>\u2014that\u00a0is, new\u00a0materials are produced from the atoms that were present in the starting\u00a0materials which are known as <abbr title=\"To break down into its original parts; decay\">reactants<\/abbr>. The new\u00a0materials which are\u00a0formed as the result of a chemical reaction are called <abbr title=\"A starting substance in a chemical reaction; It is found to the left of the arrow.\">products<\/abbr>.\u00a0Chemical equations are a short-hand way of expressing that change in\u00a0matter\u00a0using chemical symbols. A chemical reaction is considered balanced when\u00a0there\u00a0are equal numbers of each kind of atom on both sides of the equation.\u00a0Because\u00a0chemists believe in <abbr title=\"Matter can be neither created nor destroyed in an ordinary chemical or physical process.\">the law of conservation of mass<\/abbr>,\u00a0equations must be\u00a0balanced in order to correctly show the changes which have occurred.<\/p>\n<p>For example, when sodium\u00a0metal is placed in a container\u00a0with chlorine gas a chemical change occurs, as can be noted by the\u00a0disappearance of the metal and the yellow-green gas and the appearance of a\u00a0white crystalline solid called sodium chloride in the container. Sparks\u00a0fly,\u00a0heat is given off. The properties of the new material are quite\u00a0different from\u00a0the properties of the starting materials.<\/p>\n<p>Some of the clues which\u00a0signify that a chemical change\u00a0has occurred are:<\/p>\n<ul>\n<li>The formation of new materials, recognizable by\u00a0different colors<\/li>\n<li>The\u00a0disappearance of starting materials<\/li>\n<li>A\u00a0change in energy as evidenced by production of\u00a0light or sound<\/li>\n<li>An\u00a0increase or decrease in the temperature<\/li>\n<\/ul>\n<p>The chemical equation for the above reaction would be:<\/p>\n<p class=\"center\">Na(<em>s<\/em>)\u00a0+ Cl<sub>2<\/sub>(<em>g<\/em>) \u2192 NaCl(<em>s<\/em>)<\/p>\n<p>In order to balance the\u00a0equation, a <abbr title=\"The number written in front of a reactant or product of a chemical reaction; It tells the smallest number of particles of the substance involved in the reaction.\">coefficient<\/abbr> can be placed in front of both the Na(<em>s<\/em>) and the NaCl(<em>s<\/em>) which\u00a0corrects the unbalance between the atoms.<\/p>\n<p class=\"center\">2Na(<em>s<\/em>)\u00a0+\u00a0Cl<sub>2<\/sub>(<em>g<\/em>) \u2192 2NaCl(<em>s<\/em>)<\/p>\n<p>There are generally five different types of chemical changes that occur in matter. There are other ways to subgroup these changes in matter, but most chemical reactions can be placed into one of the following five groups:<\/p>\n<ul>\n<li>Combination or synthesis reactions<\/li>\n<li>Decomposition reactions<\/li>\n<li>Single replacement or single displacement reactions<\/li>\n<li>Double replacement (displacement) or metathesis reactions<\/li>\n<li>Combustion reactions<\/li>\n<\/ul>\n<p>Synthesis reactions have two or more reactants combining to produce a single product which is a compound. A new compound is created by the direct combination of reactants. The reaction of hydrogen gas with oxygen gas to produce water is such a reaction.<\/p>\n<p>Decomposition reactions are the chemical opposite of synthesis reactions. In decomposition reactions one reactant, which must be a compound, comes apart to form simpler substances which may be elements or compounds. Most decomposition reactions require energy to proceed. Such reactions are also classified as <abbr title=\"A chemical reaction in which a greater amount of energy is required to break the existing bonds in the reactants than is released when the new bonds form in the product molecules\">endothermic<\/abbr>. An example of a decomposition reaction is the heating of solid calcium carbonate, CaCO<sub>3<\/sub>(<em>s<\/em>) to form solid calcium oxide, CaO(<em>s<\/em>) and carbon dioxide gas, CO<sub>2<\/sub>(<em>g<\/em>).<\/p>\n<p>Displacement reactions are sometimes called replacement reactions. Single displacement reactions always have an element and a compound as reactants. The element which was a reactant ends up in a compound which is a product. The element that was produced in the reaction was originally in the compound. Many of these reactions must occur in solution, but not always. If copper metal is placed in a solution of silver nitrate in a beaker, a single replacement reaction occurs. Silver metal forms in the beaker while the solution which was originally colorless begins to take on the blue color characteristic of copper(II) ion. The copper metal has taken the place of the silver ion in the solution; the silver ion becomes silver metal in the beaker. The balanced equation for this reaction is<\/p>\n<p class=\"center\">Cu(<em>s<\/em>) + 2AgNO<sub>3<\/sub>(<em>aq<\/em>) \u2192 Cu(NO<sub>3<\/sub>)<sub>2<\/sub>(<em>aq<\/em>) + 2Ag(<em>s<\/em>)<\/p>\n<p>Double replacement reactions, which are sometimes called metathesis reactions, are characterized by having two compounds as reactants and two compounds as products. The reactants are both ionic compounds in solution. In this type of reaction, the <abbr title=\" Positively charged particles\">cations<\/abbr> of the reactants exchange <abbr title=\"Negatively charged particles\">anions<\/abbr>; the products are new compounds one of which must be insoluble, a gas or a <abbr title=\"A substance which ionizes only partially in aqueous solution\">weak electrolyte<\/abbr> such as water. If all products are soluble ionic compounds, there will be no reaction. For example, if aqueous solutions of silver nitrate and sodium chloride are mixed, a double replacement reaction occurs producing soluble sodium nitrate and insoluble silver chloride. In equation form,<\/p>\n<p class=\"center\">AgNO<sub>3<\/sub>(<em>aq<\/em>) + NaCl(<em>aq<\/em>) \u2192 NaNO<sub>3<\/sub>(<em>aq<\/em>) + AgCl(<em>s<\/em>)<\/p>\n<p>The last type of reaction is the combustion reaction which involves the reaction of oxygen with either an element or a compound, which is usually a <abbr title=\"Simplest organic compound composed only of carbon and hydrogen\">hydrocarbon<\/abbr>. If the reaction is between an element and oxygen, and only the oxide of the element is formed, the reaction may also be considered to be a synthesis reaction. Typical combustion reactions of <abbr title=\"All compounds that contain carbon with the primary exceptions of carbon oxides, carbides and carbonates, all of which are considered inorganic\">organic compounds<\/abbr> can be recognized by the products of carbon dioxide and water. Reactants such as <abbr title=\"Organic molecules containing a hydroxyl group -OH attached to a carbon chain \">alcohols<\/abbr>, <abbr title=\" Compound containing multiple hydroxyl (OH-) groups, plus an aldehyde or ketone functional group (The hydrogen and oxygen are present in a 2:1 ratio.)\">carbohydrates<\/abbr>, <abbr title=\"Their molecules contain an oxygen atom doubly bonded to a carbon and that same carbon needs to have carbon atoms attached to both sides of it. In practice, that means the double bonded oxygen atom is not on the end of the chain. \">ketones<\/abbr>, <abbr title=\"Saturated hydrocarbons which contain only single bonds\">alkanes<\/abbr>, <abbr title=\"Hydrocarbons that contain one or more double bonds\">alkenes<\/abbr> and <abbr title=\"A special group of unsaturated cyclic hydrocarbons with delocalized electrons\">aromatics<\/abbr> will produce water and carbon dioxide as products if the combustion is complete. If insufficient oxygen is present for complete combustion, carbon monoxide will be formed. In any case, oxygen is always a reactant.<\/p>\n<p>Ethanol, C<sub>2<\/sub>H<sub>5<\/sub>OH(<em>l<\/em>), burns in oxygen to produce water and carbon dioxide according to the balanced equation:<\/p>\n<p class=\"center\">C<sub>2<\/sub>H<sub>5<\/sub>OH(<em>l<\/em>) + 3O<sub>2<\/sub>(<em>g<\/em>)<img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/chemistry\/wp-content\/uploads\/sites\/3\/2017\/08\/arrow.gif\" width=\"20\" height=\"14\" \/>2CO<sub>2<\/sub>(<em>g<\/em>) + 3H<sub>2<\/sub>O(<em>l<\/em>)<\/p>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>In the following list of equations, how many are replacement reactions?<\/p>\n<p>2H<sub>2<\/sub> + O<sub>2<\/sub> \u2192 2 H<sub>2<\/sub>O<\/p>\n<p>Zn + CuCl<sub>2<\/sub> \u2192 Cu + ZnCl<sub>2<\/sub><\/p>\n<p>HCl + NaOH \u2192 NaCl + H<sub>2<\/sub>O<\/p>\n<p>CuCO<sub>3<\/sub> \u2192 CuO + CO<sub>2<\/sub><\/p>\n<p>CH<sub>4<\/sub> + 2O<sub>2<\/sub> \u2192 CO<sub>2<\/sub> + 2H<sub>2<\/sub>O<\/p>\n<ol>\n<li>none<\/li>\n<li>one<\/li>\n<li>two<\/li>\n<li>three<\/li>\n<\/ol>\n<p><a class=\"button button-primary q-answer\"> Reveal Answer <\/a><\/p>\n<p class=\"q-reveal\">The correct answer is C. Both the second and third equations are types of replacement reactions. The second equation is a single replacement while the third equation is a double replacement reaction.<\/p>\n<\/section>\n<h3>Predicting Products of Reactions<\/h3>\n<p>The products of reactions\u00a0can be predicted by recognizing\u00a0the pattern of reactants in the equation.\u00a0Synthesis reactions have two or more reactants and a\u00a0single product. Synthesis reactions are simply the direct combination\u00a0of the\u00a0reactants.<\/p>\n<p class=\"center\">2Na + Br<sub>2<\/sub> \u2192 2NaBr<\/p>\n<p>Decomposition reactions have\u00a0a single reactant and\u00a0several products. Decomposition reactions break down the initial\u00a0compound into\u00a0simpler substances which may not be the elements of the compound. For\u00a0example, \u00a0heating CuCO<sub>3<\/sub> produces carbon dioxide and CuO\u00a0not Cu, C and O<sub>2<\/sub>.\u00a0Take time to learn some well known\u00a0decomposition reactions and\u00a0don\u2019t assume that\u00a0the elements are directly produced by heating a compound.\u00a0Some\u00a0typical\u00a0decomposition reactions:<\/p>\n<ol>\n<li>Metallic\u00a0carbonates, when heated, form metallic oxides and CO<sub>2<\/sub>(<em>g<\/em>). Ex. CaCO<sub>3<\/sub>(<em>s<\/em>) \u2192 CaO(<em>s<\/em>)\u00a0+ \u00a0CO<sub>2<\/sub>(<em>g<\/em>)<\/li>\n<li>Most metallic\u00a0hydroxides, when heated, decompose into metallic oxides and water. Ex. Ca(OH)<sub>2<\/sub>(<em>s<\/em>) \u2192 CaO(<em>s<\/em>) H<sub>2<\/sub>O(<em>g<\/em>)<\/li>\n<li>Metallic\u00a0chlorates, when heated, decompose into metallic chlorides and oxygen. Ex. 2KClO<sub>3<\/sub>(<em>s<\/em>) \u2192 2KCl(<em>s<\/em>) + 3O<sub>2<\/sub>(<em>g<\/em>)<\/li>\n<li>Some acids,\u00a0when heated, decompose into nonmetallic oxides and water. Ex. H<sub>2<\/sub>SO<sub>4<\/sub>(<em>l<\/em>) \u2192 H<sub>2<\/sub>O(<em>l<\/em>)\u00a0+ \u00a0SO<sub>3<\/sub>(<em>g<\/em>)<\/li>\n<li>Some oxides,\u00a0when heated, decompose. Ex. 2HgO(<em>s<\/em>) \u2192 2Hg(<em>l<\/em>)\u00a0+\u00a0O<sub>2<\/sub>(<em>g<\/em>)<\/li>\n<li>Some decomposition reactions are produced by electrical currents. Ex. 2H<sub>2<\/sub>O(<em>l<\/em>) \u2192 2H<sub>2<\/sub>(<em>g<\/em>)\u00a0+ \u00a0O<sub>2<\/sub>(<em>g<\/em>) Ex. 2NaCl(<em>l<\/em>) \u2192 2Na(<em>s<\/em>) \u00a0+\u00a0Cl<sub>2<\/sub>(<em>g<\/em>)<\/li>\n<\/ol>\n<p>The products of single replacement reactions can be predicted because the free element, which was a reactant, is found in the compound after the reaction occurs; the element which was in the compound is replaced and is found as the free element.<\/p>\n<p>If iron metal is placed in\u00a0an aqueous solution of\u00a0copper(II) chloride, what will the products be?<\/p>\n<p>The iron is the free\u00a0element\u00a0and will end up in the new compound replacing the copper which will be\u00a0found as\u00a0a free element in the beaker. The equation can be written as\u00a0Fe(<em>s<\/em>)\u00a0+\u00a0CuCl<sub>2<\/sub>(<em>aq<\/em>) \u2192 Cu(<em>s<\/em>) +\u00a0FeCl<sub>2<\/sub>(<em>aq<\/em>)\u00a0Single replacement reactions only occur if the reactant metal is more active,\u00a0based on activity charts, than the one in the reactant compound. An activity\u00a0chart is\u00a0shown below. We will discuss more about activities of metals later in the\u00a0course.<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/chemistry\/wp-content\/uploads\/sites\/3\/2017\/08\/classifychemreactions6.activity_series.gif\" alt=\"Activity chart of metals\" \/><\/center><\/p>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>Which of the following reactions can be classified in more than one category?<\/p>\n<ol>\n<li>2Mg + O<sub>2<\/sub> \u2192 MgO<\/li>\n<li>Mg + CuBr<sub>2<\/sub> \u2192 Cu + MgBr<sub>2<\/sub><\/li>\n<li>Mg(OH)<sub>2<\/sub> + H<sub>2<\/sub>SO<sub>4<\/sub> \u2192 MgSO<sub>4<\/sub>+ 2H<sub>2<\/sub>O<\/li>\n<li>2H<sub>2<\/sub>O<sub>2<\/sub> \u2192 2H<sub>2<\/sub>O+ O<sub>2<\/sub><\/li>\n<\/ol>\n<p><a class=\"button button-primary q-answer\"> Reveal Answer <\/a><\/p>\n<p class=\"q-reveal\">The correct answer is A. That is because it is both a synthesis and a combustion reaction.<\/p>\n<\/section>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>The reaction CaO + H<sub>2<\/sub>O \u2192 Ca(OH)<sub>2<\/sub> would be classified as<\/p>\n<ol>\n<li>synthesis<\/li>\n<li>decomposition<\/li>\n<li>single replacement<\/li>\n<li>double replacement<\/li>\n<\/ol>\n<p><a class=\"button button-primary q-answer\"> Reveal Answer <\/a><\/p>\n<p class=\"q-reveal\">The correct answer is A. That is because only one substance is produced in the reaction. In synthesis reactions, the product is always one substance.loride will not attract one another.<\/p>\n<\/section>\n<\/section>\n<p><!-- CONTENT ENDS HERE --><\/p>\n<p><!-- UPDATE NEXT\/PREVIOUS BELOW --><\/p>\n<div class=\"advance\">\n<p><a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/reactions-and-reactivity\">Workshop Index<\/a>\u00a0<a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/chemistry\/types-of-chemical-equations\">Next Lesson\u00a0\u27a1<\/a><\/p>\n<\/div>\n<p><a class=\"backtotop\" href=\"#title\">Back to Top<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Workshop Index\u00a0Next Lesson\u00a0\u27a1 Classifying Chemical Reactions and Predicting Products Objective In this lesson, we will review different types of\u00a0chemical reactions and discuss how to predict the products of a\u00a0reaction based\u00a0upon the type of chemical reaction that will occur. Classifying Chemical Reactions Chemical reactions occur\u00a0when substances combine or decompose forming new types of chemical substances with [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-383","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/pages\/383","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/comments?post=383"}],"version-history":[{"count":18,"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/pages\/383\/revisions"}],"predecessor-version":[{"id":985,"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/pages\/383\/revisions\/985"}],"wp:attachment":[{"href":"https:\/\/americanboard.org\/Subjects\/chemistry\/wp-json\/wp\/v2\/media?parent=383"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}