{"id":7639,"date":"2021-06-08T21:57:08","date_gmt":"2021-06-08T21:57:08","guid":{"rendered":"https:\/\/opentextbc.ca\/introductorychemistry\/chapter\/chemical-equilibrium\/"},"modified":"2021-10-07T20:21:28","modified_gmt":"2021-10-07T20:21:28","slug":"chemical-equilibrium","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/introductorychemistry\/chapter\/chemical-equilibrium\/","title":{"raw":"Chemical Equilibrium","rendered":"Chemical Equilibrium"},"content":{"raw":"
\r\n

Learning Objectives<\/p>\r\n\r\n<\/header>\r\n

\r\n
    \r\n \t
  1. Define chemical equilibrium<\/em>.<\/li>\r\n \t
  2. Recognize chemical equilibrium as a dynamic process.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\nConsider the following reaction occurring in a closed container (so that no material can go in or out):\r\n

    H2<\/sub> +\u00a0I2<\/sub> \u2192\u00a02HI<\/p>\r\nThis is simply the reaction between elemental hydrogen and elemental iodine to make hydrogen iodide. The way the equation is written, we are led to believe that the reaction goes to completion, that all the H2<\/sub> and the I2<\/sub> react to make HI.\r\n\r\nHowever, this is not the case. The reverse chemical reaction is also taking place:\r\n

    2HI \u2192 H2<\/sub> +\u00a0I2<\/sub><\/p>\r\nIt acts to undo what the first reaction does. Eventually, the reverse reaction proceeds so quickly that it matches the speed of the forward reaction. When that happens, any continued overall reaction stops: the reaction has reached chemical equilibrium<\/strong>\u00a0(sometimes just spoken as equilibrium<\/em>; plural equilibria<\/em>), the point at which the forward and reverse processes balance each other\u2019s progress.\r\n\r\nBecause two opposing processes are occurring at once, it is conventional to represent an equilibrium using a double arrow, like this:\r\n

    H2\u00a0<\/sub>+\u00a0I2\u00a0<\/sub>\u21c4 2HI<\/p>\r\n

    The double arrow implies that the reaction is going in both directions. Note that the reaction must still be balanced.<\/p>\r\n\r\n

    \r\n

    Example 13.1<\/p>\r\n\r\n<\/header>\r\n

    \r\n\r\nWrite the equilibrium equation that exists between calcium carbonate as a reactant and calcium oxide and carbon dioxide as products.\r\n\r\nSolution<\/em>\r\nAs this is an equilibrium situation, a double arrow is used. The equilibrium equation is written as follows:\r\n

    CaCO3 <\/sub>\u21c4 CaO + CO2<\/sub><\/p>\r\nTest Yourself<\/em>\r\nWrite the equilibrium equation between elemental hydrogen and elemental oxygen as reactants and water as the product.\r\n\r\nAnswer<\/em>\r\n2H2 <\/sub>+ O2<\/sub> \u21c4 2H2<\/sub>O\r\n\r\n<\/div>\r\n<\/div>\r\nOne thing to note about equilibrium is that the reactions do not stop; both the forward reaction and the reverse reaction continue to occur. They both occur at the same rate, so any overall change by one reaction is cancelled by the reverse reaction. We say that chemical equilibrium is dynamic<\/em>, rather than static. Also, because both reactions are occurring simultaneously, the equilibrium can be written backward. For example, representing an equilibrium as\r\n

    H2<\/sub>+\u00a0I2\u00a0<\/sub>\u21c4 2HI<\/p>\r\nis the same thing as representing the same equilibrium as\r\n

    2HI \u21c4 H2\u00a0<\/sub>+\u00a0I2<\/sub><\/p>\r\nThe reaction must be at equilibrium for this to be the case, however.\r\n

    \r\n

    Key Takeaways<\/p>\r\n\r\n<\/header>\r\n

    \r\n
      \r\n \t
    • Chemical reactions eventually reach equilibrium, a point at which forward and reverse reactions balance each other\u2019s progress.<\/li>\r\n \t
    • Chemical equilibria are dynamic: the chemical reactions are always occurring; they just cancel each other\u2019s progress.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
      \r\n

      Exercises<\/p>\r\n\r\n<\/header>\r\n

      \r\n

      Questions<\/h1>\r\n
        \r\n \t
      1. Define chemical equilibrium<\/em>. Give an example.<\/li>\r\n \t
      2. Explain what is meant when it is said that chemical equilibrium is dynamic.<\/li>\r\n \t
      3. Write the equilibrium equation between elemental hydrogen and elemental chlorine as reactants and hydrochloric acid as the product.<\/li>\r\n \t
      4. Write the equilibrium equation between iron(III) sulfate as the reactant and iron(III) oxide and sulfur trioxide as the products.<\/li>\r\n \t
      5. Graphite and diamond are two forms of elemental carbon. Write the equilibrium equation between these two forms in two different ways.<\/li>\r\n \t
      6. At 1,500 K, iodine molecules break apart into iodine atoms. Write the equilibrium equation between these two species in two different ways.<\/li>\r\n<\/ol>\r\n

        Answers<\/h1>\r\n
          \r\n \t
        1. The situation when the forward and reverse chemical reactions occur, leading to no additional net change in the reaction position; H2<\/sub>+ I2<\/sub> \u21c4 2HI (answers will vary)<\/li>\r\n<\/ol>\r\n
            \r\n \t
          1. H2<\/sub> + Cl2<\/sub> \u21c4 2HCl<\/li>\r\n<\/ol>\r\n
              \r\n \t
            1. C\u00a0(gra) \u21c4 C\u00a0(dia);\u00a0C\u00a0(dia) \u21c4 C\u00a0(gra)<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>","rendered":"
              \n
              \n

              Learning Objectives<\/p>\n<\/header>\n

              \n
                \n
              1. Define chemical equilibrium<\/em>.<\/li>\n
              2. Recognize chemical equilibrium as a dynamic process.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n

                Consider the following reaction occurring in a closed container (so that no material can go in or out):<\/p>\n

                H2<\/sub> +\u00a0I2<\/sub> \u2192\u00a02HI<\/p>\n

                This is simply the reaction between elemental hydrogen and elemental iodine to make hydrogen iodide. The way the equation is written, we are led to believe that the reaction goes to completion, that all the H2<\/sub> and the I2<\/sub> react to make HI.<\/p>\n

                However, this is not the case. The reverse chemical reaction is also taking place:<\/p>\n

                2HI \u2192 H2<\/sub> +\u00a0I2<\/sub><\/p>\n

                It acts to undo what the first reaction does. Eventually, the reverse reaction proceeds so quickly that it matches the speed of the forward reaction. When that happens, any continued overall reaction stops: the reaction has reached chemical equilibrium<\/strong>\u00a0(sometimes just spoken as equilibrium<\/em>; plural equilibria<\/em>), the point at which the forward and reverse processes balance each other\u2019s progress.<\/p>\n

                Because two opposing processes are occurring at once, it is conventional to represent an equilibrium using a double arrow, like this:<\/p>\n

                H2\u00a0<\/sub>+\u00a0I2\u00a0<\/sub>\u21c4 2HI<\/p>\n

                The double arrow implies that the reaction is going in both directions. Note that the reaction must still be balanced.<\/p>\n

                \n
                \n

                Example 13.1<\/p>\n<\/header>\n

                \n

                Write the equilibrium equation that exists between calcium carbonate as a reactant and calcium oxide and carbon dioxide as products.<\/p>\n

                Solution<\/em>
                \nAs this is an equilibrium situation, a double arrow is used. The equilibrium equation is written as follows:<\/p>\n

                CaCO3 <\/sub>\u21c4 CaO + CO2<\/sub><\/p>\n

                Test Yourself<\/em>
                \nWrite the equilibrium equation between elemental hydrogen and elemental oxygen as reactants and water as the product.<\/p>\n

                Answer<\/em>
                \n2H2 <\/sub>+ O2<\/sub> \u21c4 2H2<\/sub>O<\/p>\n<\/div>\n<\/div>\n

                One thing to note about equilibrium is that the reactions do not stop; both the forward reaction and the reverse reaction continue to occur. They both occur at the same rate, so any overall change by one reaction is cancelled by the reverse reaction. We say that chemical equilibrium is dynamic<\/em>, rather than static. Also, because both reactions are occurring simultaneously, the equilibrium can be written backward. For example, representing an equilibrium as<\/p>\n

                H2<\/sub>+\u00a0I2\u00a0<\/sub>\u21c4 2HI<\/p>\n

                is the same thing as representing the same equilibrium as<\/p>\n

                2HI \u21c4 H2\u00a0<\/sub>+\u00a0I2<\/sub><\/p>\n

                The reaction must be at equilibrium for this to be the case, however.<\/p>\n

                \n
                \n

                Key Takeaways<\/p>\n<\/header>\n

                \n
                  \n
                • Chemical reactions eventually reach equilibrium, a point at which forward and reverse reactions balance each other\u2019s progress.<\/li>\n
                • Chemical equilibria are dynamic: the chemical reactions are always occurring; they just cancel each other\u2019s progress.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n
                  \n
                  \n

                  Exercises<\/p>\n<\/header>\n

                  \n

                  Questions<\/h1>\n
                    \n
                  1. Define chemical equilibrium<\/em>. Give an example.<\/li>\n
                  2. Explain what is meant when it is said that chemical equilibrium is dynamic.<\/li>\n
                  3. Write the equilibrium equation between elemental hydrogen and elemental chlorine as reactants and hydrochloric acid as the product.<\/li>\n
                  4. Write the equilibrium equation between iron(III) sulfate as the reactant and iron(III) oxide and sulfur trioxide as the products.<\/li>\n
                  5. Graphite and diamond are two forms of elemental carbon. Write the equilibrium equation between these two forms in two different ways.<\/li>\n
                  6. At 1,500 K, iodine molecules break apart into iodine atoms. Write the equilibrium equation between these two species in two different ways.<\/li>\n<\/ol>\n

                    Answers<\/h1>\n
                      \n
                    1. The situation when the forward and reverse chemical reactions occur, leading to no additional net change in the reaction position; H2<\/sub>+ I2<\/sub> \u21c4 2HI (answers will vary)<\/li>\n<\/ol>\n
                        \n
                      1. H2<\/sub> + Cl2<\/sub> \u21c4 2HCl<\/li>\n<\/ol>\n
                          \n
                        1. C\u00a0(gra) \u21c4 C\u00a0(dia);\u00a0C\u00a0(dia) \u21c4 C\u00a0(gra)<\/li>\n<\/ol>\n<\/div>\n<\/div>\n","protected":false},"author":90,"menu_order":1,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-7639","chapter","type-chapter","status-publish","hentry"],"part":7638,"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/pressbooks\/v2\/chapters\/7639","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/wp\/v2\/users\/90"}],"version-history":[{"count":5,"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/pressbooks\/v2\/chapters\/7639\/revisions"}],"predecessor-version":[{"id":8957,"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/pressbooks\/v2\/chapters\/7639\/revisions\/8957"}],"part":[{"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/pressbooks\/v2\/parts\/7638"}],"metadata":[{"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/pressbooks\/v2\/chapters\/7639\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/wp\/v2\/media?parent=7639"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/pressbooks\/v2\/chapter-type?post=7639"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/wp\/v2\/contributor?post=7639"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/introductorychemistry\/wp-json\/wp\/v2\/license?post=7639"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}