{"id":78,"date":"2024-10-24T19:39:40","date_gmt":"2024-10-24T23:39:40","guid":{"rendered":"https:\/\/sites.temple.edu\/chemdemo\/?p=78"},"modified":"2024-10-25T16:22:01","modified_gmt":"2024-10-25T20:22:01","slug":"chemical-equilibrium","status":"publish","type":"post","link":"https:\/\/sites.temple.edu\/chemdemo\/2024\/10\/24\/chemical-equilibrium\/","title":{"rendered":"Chemical Equilibrium"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\">Purpose<\/h2>\n\n\n\n<p>To show the effect of <strong>temperature<\/strong> on the equilibrium of NO2 and N2O4<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Procedure<\/h2>\n\n\n\n<p>Follow the Flinn Procedure.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Reaction<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>NO2 Equilibrium:<\/strong><br>2NO2(g)\u21ccN2O4(g)+N2O3(s)+NO(g)<\/li>\n\n\n\n<li>Colors: Brown (NO2) \u2194 Colorless (N2O4, NO3)<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Thermodynamic Data<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Standard Enthalpy (\u0394 H\u00b0):<\/strong> -57.2 kJ<\/li>\n\n\n\n<li><strong>Standard Entropy (\u0394 S\u00b0):<\/strong> -175.83 J\/mol-K<\/li>\n<\/ul>\n\n\n\n<h4 class=\"wp-block-heading\">Standard-State Enthalpies of Formation and Entropies<\/h4>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Compound<\/th><th>(\u0394H\u00b0<sub>f<\/sub>) (kJ\/mol)<\/th><th>(\u0394S\u00b0) (J\/mol-K)<\/th><\/tr><\/thead><tbody><tr><td>NO2<\/td><td>33.18<\/td><td>240.06<\/td><\/tr><tr><td>N2O4<\/td><td>9.16<\/td><td>304.29<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Gibbs Free Energy and Equilibrium Constant<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Temperature (\u00b0C)<\/th><th>(\u0394G\u00b0) (kJ)<\/th><th>(K<sub>p<\/sub>)<\/th><\/tr><\/thead><tbody><tr><td>100<\/td><td>8.4<\/td><td>0.066<\/td><\/tr><tr><td>0<\/td><td>-9.2<\/td><td>58<\/td><\/tr><tr><td>-78<\/td><td>-22.9<\/td><td>1.3 x 10^6<\/td><\/tr><tr><td>-196<\/td><td>-43.6<\/td><td>3.7 x 10^29<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Approximation<\/h3>\n\n\n\n<p>The temperature dependence of (\u0394H\u00b0) is small, allowing for estimation of the equilibrium constant at various temperatures.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">Cobalt Chloride Equilibrium<\/h1>\n\n\n\n<h2 class=\"wp-block-heading\">Overview<\/h2>\n\n\n\n<p>The equilibrium between [Co(H2O)6]\u00b2\u207a and [CoCl4]\u00b2\u207b in aqueous solution demonstrates the effect of concentration and temperature on chemical equilibrium.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Reaction Equation<\/h3>\n\n\n\n<p>[Co(H<sub>2<\/sub>O)<sub>6<\/sub>]<sup>2+<\/sup> (aq) + 4 Cl<sup>\u2212<\/sup> (aq) \u21cc [CoCl<sub>4<\/sub>]<sup>2\u2212<\/sup> (aq) + 6 H<sub>2<\/sub>O (l)<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Color Changes<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Pink:<\/strong> [Co(H<sub>2<\/sub>O)<sub>6<\/sub>]\u00b2\u207a<\/li>\n\n\n\n<li><strong>Blue:<\/strong> [CoCl<sub>4<\/sub>]\u00b2\u207b<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Discussion<\/h3>\n\n\n\n<p>This demonstration visually illustrates reversible reactions and the effects of <strong>concentration<\/strong> and <strong>temperature<\/strong> on equilibrium, reinforcing Le Chatelier\u2019s principle.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Apparatus and Chemicals<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Apparatus:<\/strong><\/li>\n\n\n\n<li>Eye protection<\/li>\n\n\n\n<li>6 Boiling tubes<\/li>\n\n\n\n<li>1 or 2 Racks for boiling tubes<\/li>\n\n\n\n<li>100 cm\u00b3 Measuring cylinder<\/li>\n\n\n\n<li>3 Beakers (250 cm\u00b3)<\/li>\n\n\n\n<li>2 Dropping pipettes<\/li>\n\n\n\n<li>Access to a top-pan balance<\/li>\n\n\n\n<li><strong>Chemicals:<\/strong><\/li>\n\n\n\n<li>Cobalt(II) chloride-6-water (CoCl2\u00b76H2O) &#8211; 4.0 g (Toxic, Dangerous for the environment)<\/li>\n\n\n\n<li>Concentrated hydrochloric acid &#8211; 100 cm\u00b3 (Corrosive)<\/li>\n\n\n\n<li>Crushed ice &#8211; ~200 cm\u00b3<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Safety Notes<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Refer to CLEAPSS Hazcards for CoCl2\u00b76H2O and concentrated HCl.<\/li>\n\n\n\n<li>Avoid skin contact with cobalt(II) chloride and wash hands after use.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Procedure<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Preparation<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Boil water in a beaker and prepare crushed ice in a separate beaker.<\/li>\n\n\n\n<li>Dissolve 4 g of CoCl2\u00b76H2O in 40 mL of water to form a reddish-pink solution (label as TOXIC).<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\">Demonstration Steps<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Mixing Solution:<\/strong><\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Add 60 mL concentrated HCl to the pink solution to form a violet solution.<\/li>\n\n\n\n<li>Adjust with HCl or water to create an &#8216;in-between&#8217; violet solution for six boiling tubes.<\/li>\n<\/ul>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Effect of Concentration:<\/strong><\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use one tube as a control.<\/li>\n\n\n\n<li>Add water to the second tube (changes to pink) and HCl to the third (changes to blue).<\/li>\n\n\n\n<li>Demonstrate reversibility by adjusting HCl and water.<\/li>\n<\/ul>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Effect of Temperature:<\/strong><\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use three tubes of violet solution, with one as control.<\/li>\n\n\n\n<li>Place one tube in hot water (turns blue) and another in ice\/water mixture (turns pink).<\/li>\n\n\n\n<li>Show reversibility by swapping tubes.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Teaching Notes<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The color change of cobalt complexes forms the basis for cobalt chloride indicator papers and self-indicating silica gel desiccants.<\/li>\n\n\n\n<li>The reaction is endothermic; raising temperature shifts equilibrium right (more blue complex).<\/li>\n\n\n\n<li>Adding HCl increases chloride ion concentration, shifting equilibrium right; adding water decreases it, shifting left.<\/li>\n\n\n\n<li>An extension activity could involve using sodium chloride to observe equilibrium shifts.<\/li>\n<\/ul>\n\n\n\n<h1 class=\"wp-block-heading\">Thionin Equilibrium<\/h1>\n\n\n\n<h2 class=\"wp-block-heading\">Purpose<\/h2>\n\n\n\n<p>To demonstrate the effect of <strong>light<\/strong> on an equilibrium.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Procedure<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Follow the Flinn Procedure.<\/strong><\/li>\n\n\n\n<li><strong>Cooling Setup:<\/strong>\n<ul class=\"wp-block-list\">\n<li>Prepare a dry ice\/alcohol slurry bath.<\/li>\n\n\n\n<li>Cool each tube in the slurry, ensuring one tube is left in the bath longer than the other.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Warming:<\/strong>\n<ul class=\"wp-block-list\">\n<li>After cooling, allow the tubes to warm back up to room temperature.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Purpose To show the effect of temperature on the equilibrium of NO2 and N2O4 Procedure Follow the Flinn Procedure. Reaction Thermodynamic Data Standard-State Enthalpies of&#8230;<\/p>\n<div class=\"more-link-wrapper\"><a class=\"more-link\" href=\"https:\/\/sites.temple.edu\/chemdemo\/2024\/10\/24\/chemical-equilibrium\/\">Continue Reading<span class=\"screen-reader-text\">Chemical Equilibrium<\/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-78","post","type-post","status-publish","format-standard","hentry","category-demonstrations","entry"],"_links":{"self":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/78","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=78"}],"version-history":[{"count":4,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/78\/revisions"}],"predecessor-version":[{"id":82,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/posts\/78\/revisions\/82"}],"wp:attachment":[{"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/media?parent=78"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/categories?post=78"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sites.temple.edu\/chemdemo\/wp-json\/wp\/v2\/tags?post=78"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}