{"id":3239,"date":"2016-08-25T19:41:46","date_gmt":"2016-08-25T19:41:46","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/?post_type=chapter&#038;p=3239"},"modified":"2017-08-31T17:49:59","modified_gmt":"2017-08-31T17:49:59","slug":"mechanisms-and-potential-energy-diagrams","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/chapter\/mechanisms-and-potential-energy-diagrams\/","title":{"raw":"Mechanisms and Potential Energy Diagrams","rendered":"Mechanisms and Potential Energy Diagrams"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<div>\r\n<ul>\r\n \t<li>Draw and label a potential energy diagram for a two-step reaction.<\/li>\r\n \t<li>Describe the use of a potential energy diagram for identifying the rate-limiting step in a multi-step reaction.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox examples\">\r\n<h3>Roller coasters-fun or frightful?<\/h3>\r\n[caption id=\"\" align=\"aligncenter\" width=\"600\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/53\/2014\/08\/19212922\/20140811155716480429.jpeg\" alt=\"Nighttime roller coaster. The slowest peak in a roller coaster ride is the tallest peak and is the rate determining step\" width=\"600\" height=\"268\" \/> Roller Coaster. From Greg Bulla (<a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:MissionBeachRollercoaster_640pixels.JPG\">Wikipedia<\/a>: Gb1).[\/caption]\r\n\r\nFor many people, a roller coaster is the epitome of excitement, while for others it is a torture device to be avoided at all costs (and some folks are in-between). For a roller coaster, the rate-limiting step is the climb up to the top at the beginning of the ride, where the cars are hauled slowly to the peak of the ride. This peak must be the highest because the potential energy at this point must be enough to cause the roller coaster to move through the smaller peaks without stopping.\r\n\r\n<\/div>\r\n<h2>Potential Energy Diagrams<\/h2>\r\nThe potential energy diagram can illustrate the mechanism for a reaction by showing each elementary step of the reaction with distinct activation energy (see <strong> Figure <\/strong> below ).\r\n<div>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"500\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/53\/2014\/08\/19212923\/20140811155716776505.png\" alt=\"A potential energy diagram illustrates the course of a reaction across each elementary step\" width=\"500\" height=\"386\" longdesc=\"The%20potential%20energy%20diagram%20shows%20an%20activation%20energy%20peak%20for%20each%20of%20the%20elementary%20steps%20of%20the%20reaction.%20The%20valley%20between%20represents%20the%20intermediate%20for%20the%20reaction.\" \/> Figure 1. The potential energy diagram shows an activation energy peak for each of the elementary steps of the reaction. The valley between represents the intermediate for the reaction. From the CK-12 Foundation - Christopher Auyeung.[\/caption]\r\n\r\n<\/div>\r\nThe reaction whose potential energy diagram is shown in the figure is a two-step reaction. The activation energy for each step is labeled E<sub>a1 <\/sub> and E<sub>a2<\/sub>. Each elementary step has its own activated complex, labeled AC<sub>1 <\/sub> and AC<sub>2<\/sub>. Note that the overall enthalpy change of the reaction [latex]\\left(\\Delta{H}\\right)[\/latex]\u00a0is unaffected by the individual steps, since it depends only on the initial and final states.\r\n\r\nIn this example, the rate-limiting step in the reaction is the first step, leading to the formation of the activated complex AC<sub>1<\/sub>. The activation energy is higher for this step than for step two, which has a considerably lower activation energy. If the rate-limiting step were the second step, the peak labeled AC<sub>2 <\/sub> would be higher than the peak for AC<sub>1 <\/sub> and E<sub>a2 <\/sub> would be greater than E<sub>a1 <\/sub> . The same approach can be taken for a potential energy diagram with more than two peaks.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Summary<\/h3>\r\n<ul>\r\n \t<li>A potential energy diagram for a two-step reaction is shown and labeled.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Review<\/h3>\r\n<ol>\r\n \t<li>What does a potential energy diagram tell us?<\/li>\r\n \t<li>In the diagram above, which step has the highest activation energy?<\/li>\r\n \t<li>If a catalyst lowered the step one activation energy to a value lower than the step two activation energy, which step would be rate-limiting?<\/li>\r\n<\/ol>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<div>\n<ul>\n<li>Draw and label a potential energy diagram for a two-step reaction.<\/li>\n<li>Describe the use of a potential energy diagram for identifying the rate-limiting step in a multi-step reaction.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"textbox examples\">\n<h3>Roller coasters-fun or frightful?<\/h3>\n<div style=\"width: 610px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/53\/2014\/08\/19212922\/20140811155716480429.jpeg\" alt=\"Nighttime roller coaster. The slowest peak in a roller coaster ride is the tallest peak and is the rate determining step\" width=\"600\" height=\"268\" \/><\/p>\n<p class=\"wp-caption-text\">Roller Coaster. From Greg Bulla (<a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:MissionBeachRollercoaster_640pixels.JPG\">Wikipedia<\/a>: Gb1).<\/p>\n<\/div>\n<p>For many people, a roller coaster is the epitome of excitement, while for others it is a torture device to be avoided at all costs (and some folks are in-between). For a roller coaster, the rate-limiting step is the climb up to the top at the beginning of the ride, where the cars are hauled slowly to the peak of the ride. This peak must be the highest because the potential energy at this point must be enough to cause the roller coaster to move through the smaller peaks without stopping.<\/p>\n<\/div>\n<h2>Potential Energy Diagrams<\/h2>\n<p>The potential energy diagram can illustrate the mechanism for a reaction by showing each elementary step of the reaction with distinct activation energy (see <strong> Figure <\/strong> below ).<\/p>\n<div>\n<div style=\"width: 510px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/53\/2014\/08\/19212923\/20140811155716776505.png\" alt=\"A potential energy diagram illustrates the course of a reaction across each elementary step\" width=\"500\" height=\"386\" longdesc=\"The%20potential%20energy%20diagram%20shows%20an%20activation%20energy%20peak%20for%20each%20of%20the%20elementary%20steps%20of%20the%20reaction.%20The%20valley%20between%20represents%20the%20intermediate%20for%20the%20reaction.\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 1. The potential energy diagram shows an activation energy peak for each of the elementary steps of the reaction. The valley between represents the intermediate for the reaction. From the CK-12 Foundation &#8211; Christopher Auyeung.<\/p>\n<\/div>\n<\/div>\n<p>The reaction whose potential energy diagram is shown in the figure is a two-step reaction. The activation energy for each step is labeled E<sub>a1 <\/sub> and E<sub>a2<\/sub>. Each elementary step has its own activated complex, labeled AC<sub>1 <\/sub> and AC<sub>2<\/sub>. Note that the overall enthalpy change of the reaction [latex]\\left(\\Delta{H}\\right)[\/latex]\u00a0is unaffected by the individual steps, since it depends only on the initial and final states.<\/p>\n<p>In this example, the rate-limiting step in the reaction is the first step, leading to the formation of the activated complex AC<sub>1<\/sub>. The activation energy is higher for this step than for step two, which has a considerably lower activation energy. If the rate-limiting step were the second step, the peak labeled AC<sub>2 <\/sub> would be higher than the peak for AC<sub>1 <\/sub> and E<sub>a2 <\/sub> would be greater than E<sub>a1 <\/sub> . The same approach can be taken for a potential energy diagram with more than two peaks.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>Summary<\/h3>\n<ul>\n<li>A potential energy diagram for a two-step reaction is shown and labeled.<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Review<\/h3>\n<ol>\n<li>What does a potential energy diagram tell us?<\/li>\n<li>In the diagram above, which step has the highest activation energy?<\/li>\n<li>If a catalyst lowered the step one activation energy to a value lower than the step two activation energy, which step would be rate-limiting?<\/li>\n<\/ol>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-3239\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Chemistry Concepts Intermediate. <strong>Authored by<\/strong>: Calbreath, Baxter, et al.. <strong>Provided by<\/strong>: CK12.org. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/www.ck12.org\/book\/CK-12-Chemistry-Concepts-Intermediate\/\">http:\/\/www.ck12.org\/book\/CK-12-Chemistry-Concepts-Intermediate\/<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/\">CC BY-NC: Attribution-NonCommercial<\/a><\/em><\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":29,"menu_order":15,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Chemistry Concepts Intermediate\",\"author\":\"Calbreath, Baxter, et al.\",\"organization\":\"CK12.org\",\"url\":\"http:\/\/www.ck12.org\/book\/CK-12-Chemistry-Concepts-Intermediate\/\",\"project\":\"\",\"license\":\"cc-by-nc\",\"license_terms\":\"\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-3239","chapter","type-chapter","status-publish","hentry"],"part":2339,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/pressbooks\/v2\/chapters\/3239","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/wp\/v2\/users\/29"}],"version-history":[{"count":6,"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/pressbooks\/v2\/chapters\/3239\/revisions"}],"predecessor-version":[{"id":3684,"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/pressbooks\/v2\/chapters\/3239\/revisions\/3684"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/pressbooks\/v2\/parts\/2339"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/pressbooks\/v2\/chapters\/3239\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/wp\/v2\/media?parent=3239"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/pressbooks\/v2\/chapter-type?post=3239"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/wp\/v2\/contributor?post=3239"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/umes-cheminter\/wp-json\/wp\/v2\/license?post=3239"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}