{"id":43,"date":"2024-10-24T12:52:05","date_gmt":"2024-10-24T16:52:05","guid":{"rendered":"https:\/\/sites.temple.edu\/chemdemo\/?p=43"},"modified":"2024-10-25T16:22:14","modified_gmt":"2024-10-25T20:22:14","slug":"endothermic-exothermic-reactions","status":"publish","type":"post","link":"https:\/\/sites.temple.edu\/chemdemo\/2024\/10\/24\/endothermic-exothermic-reactions\/","title":{"rendered":"Endothermic &amp; Exothermic Reactions"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\">Purpose<\/h2>\n\n\n\n<p>To demonstrate that reactions can either give off heat (exothermic) or absorb heat (endothermic), emphasizing the concepts of systems and surroundings.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Materials<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Barium hydroxide octahydrate (32 g)<\/li>\n\n\n\n<li>Ammonium chloride (11 g)<\/li>\n\n\n\n<li>Small beaker<\/li>\n\n\n\n<li>Stir rod<\/li>\n\n\n\n<li>Black temperature probe (for temperatures &lt; 0\u00b0C)<\/li>\n\n\n\n<li>Piece of wood<\/li>\n\n\n\n<li>Water (for freezing the beaker)<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Procedure<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Exothermic Reaction Demonstration<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Introduction:<\/strong><\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Focus on heat flow and perform an exothermic reaction to show heat transfer to the environment.<\/li>\n\n\n\n<li>Thermite, Hydrogen Balloon, adding NaOH to water. <\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Endothermic Reaction: Barium Hydroxide and Ammonium Chloride<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Reaction Setup:<\/strong><\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Mix 32 g of barium hydroxide octahydrate with 11 g of ammonium chloride in a small beaker using a stir rod.<\/li>\n\n\n\n<li>Conduct this demonstration on a document camera for visibility.<\/li>\n<\/ul>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Observations:<\/strong><\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Encourage students to make observations, which may include:\n<ul class=\"wp-block-list\">\n<li>The odor of ammonia.<\/li>\n\n\n\n<li>Development of a liquid phase.<\/li>\n\n\n\n<li>Frosting of the glass.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Freezing the Beaker:<\/strong><\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Drip a small amount of water onto a piece of wood.<\/li>\n\n\n\n<li>Place the beaker on the drop of water for a few seconds. The beaker will freeze solidly to the wood, allowing it to be picked up.<\/li>\n\n\n\n<li>Caution: Moving the beaker prematurely will ruin the experiment.<\/li>\n<\/ul>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Discussion:<\/strong><\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use the waiting time to write the reaction equation on the board and explain the observations.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Chemical Equations<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Exothermic Dissociation of Water and Sodium Hydroxide:<\/strong><br>NaOH\u00a0(s) \u2192 Na+ (aq) + OH\u2212 (aq)<\/li>\n\n\n\n<li><strong>Endothermic Reaction Equation:<\/strong><br>Ba(OH)<sub>2<\/sub>\u200b\u22c58 H<sub>2\u200b<\/sub>O\u00a0(s) + 2 NH<sub>4<\/sub>\u200bCl\u00a0(s) \u2192 BaCl<sub>2<\/sub>\u200b\u22c52 H<sub>2<\/sub>\u200bO\u00a0(s) + 2 NH<sub>3<\/sub>\u200b (g) + 8 H<sub>2<\/sub>\u200bO\u00a0(l)<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Thermodynamic Calculations<\/h3>\n\n\n\n<p><strong>Change in Enthalpy (\u0394H<sup>\u2218<\/sup>):<\/strong><\/p>\n\n\n\n<p><strong>\u0394<\/strong>H\u00ba = { [ 1 mol \u2022 <strong>\u0394<\/strong>H<sub>f<\/sub>\u00ba(BaCl<sub>2<\/sub>\u2022 2H<sub>2<\/sub>O)<sub>(s)<\/sub> ] + [ 2 mol \u2022 <strong>\u0394<\/strong>H<sub>f<\/sub>\u00ba(NH<sub>3(aq)<\/sub>) ] + [ 8 mol \u2022 <strong>\u0394<\/strong>H<sub>f<\/sub>\u00ba(H<sub>2<\/sub>O<sub>(l)<\/sub>)]} \u2013 {[1 mol <strong>\u0394<\/strong>H<sub>f<\/sub>\u00ba(Ba(OH)<sub>2<\/sub>\u2022 8H<sub>2<\/sub>O<sub>(s)<\/sub>)] + [2 mol \u2022 <strong>\u0394<\/strong>H<sub>f<\/sub>\u00ba(NH<sub>4<\/sub>Cl)<sub>(aq)<\/sub> ] }<\/p>\n\n\n\n<p><strong>\u0394<\/strong>H\u00ba = {[1 mol \u2022 -1460.1 kJ\/mol] + [2 mol \u2022 -80.29 kJ\/mol] + [8 mol \u2022 -285.83 kJ\/mol]} \u2013 {[1 mol \u2022 -3342 kJ\/mol] + [2 mol \u2022 -314.4 kJ\/mol]}<\/p>\n\n\n\n<p><strong>\u0394<\/strong>H\u00ba = 63 kJ<\/p>\n\n\n\n<p><strong>Change in Entropy (\u0394S\u00ba):<\/strong><br><strong>\u0394<\/strong>S\u00ba = {[1 mol \u2022 S\u00ba (BaCl<sub>2<\/sub>\u2022 2H<sub>2<\/sub>O<sub>(aq)<\/sub>)] + [2 mol \u2022 S\u00ba (NH<sub>3(aq)<\/sub>)] + [8 mol \u2022 S\u00ba (H<sub>2<\/sub>O<sub>(l)<\/sub>)]} \u2013 {[1 mol \u2022 S\u00ba (Ba(OH)<sub>2<\/sub>\u2022 8H<sub>2<\/sub>O<sub>(s)<\/sub>)] + [2 mol \u2022 S\u00ba (NH<sub>4<\/sub>Cl<sub>(s)<\/sub>) ]}<\/p>\n\n\n\n<p><strong>\u0394<\/strong>S\u00ba = {[1 mol \u2022 203 J\/mol\u2022K ]+ [2 mol \u2022 111 J\/mol\u2022K] + [8 mol \u2022 69.91 J\/mol\u2022K ]}- {[1 mol \u2022 427 J\/mol\u2022K ] +[ 2 mol \u2022 94.6 J\/mol\u2022K ]}<\/p>\n\n\n\n<p><strong>\u0394<\/strong>S\u00ba = 368 J\/K<\/p>\n\n\n\n<p><strong>Change in Universal Entropy (\u0394S\u00ba<sub>univ<\/sub>):<\/strong><br><strong>\u0394<\/strong>S\u00ba<sub>univ<\/sub> = <strong>\u0394<\/strong>S\u00ba &#8211; <strong>\u0394<\/strong>H\u00ba\/T<br><strong>\u0394<\/strong>S\u00ba<sub>univ<\/sub> = [ (368 J\/K &#8211; 63 kJ)\/(273.15 + 25)K \u2022 [1000 J\/1 kJ] = <strong>157 J\/K<\/strong> &gt; 0<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Comparison to Ice Melting<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Note that when ice melts to liquid water, there is a similar increase in entropy that offsets its increase in enthalpy:<br>H<sub>2<\/sub>O (s) \u2192 H<sub>2<\/sub>O (l)<\/li>\n\n\n\n<li>Thus, this reaction is also product-favored at 25 \u00baC.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Conclusion<\/h2>\n\n\n\n<p>This experiment effectively illustrates the concepts of exothermic and endothermic reactions, demonstrating how reactions can either release or absorb heat, and emphasizes the importance of understanding systems and surroundings.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Purpose To demonstrate that reactions can either give off heat (exothermic) or absorb heat (endothermic), emphasizing the concepts of systems and surroundings. Materials Procedure Exothermic&#8230;<\/p>\n<div class=\"more-link-wrapper\"><a class=\"more-link\" href=\"https:\/\/sites.temple.edu\/chemdemo\/2024\/10\/24\/endothermic-exothermic-reactions\/\">Continue Reading<span class=\"screen-reader-text\">Endothermic &amp; Exothermic Reactions<\/span><\/a><\/div>\n","protected":false},"author":36673,"featured_media":0,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-43","post","type-post","status-publish","format-standard","hentry","category-demonstrations","entry"],"_links":{"self":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/43","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/users\/36673"}],"replies":[{"embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/comments?post=43"}],"version-history":[{"count":1,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/43\/revisions"}],"predecessor-version":[{"id":44,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/43\/revisions\/44"}],"wp:attachment":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/media?parent=43"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/categories?post=43"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/tags?post=43"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}