{"id":196627,"date":"2025-03-05T17:20:34","date_gmt":"2025-03-05T17:20:34","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=196627"},"modified":"2025-03-05T17:20:37","modified_gmt":"2025-03-05T17:20:37","slug":"the-normal-freezing-point-of-ammonia-is-78-degrees-celsius-2","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/03\/05\/the-normal-freezing-point-of-ammonia-is-78-degrees-celsius-2\/","title":{"rendered":"The normal freezing point of ammonia is -78 degrees celsius"},"content":{"rendered":"\n<p>The normal freezing point of ammonia is -78 degrees celsius. Predict the signs of Delta H, Delta S, and Delta G for ammonia when it freezes at -80 degrees celsius and 1 atm: NH3 (l) &#8212;> NH3 (s)<\/p>\n\n\n\n<p><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-6-color\">The correct answer and explanation is:<\/mark><\/strong><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Answer:<\/h3>\n\n\n\n<p>For the phase transition: NH3(l)\u2192NH3(s)\\text{NH}_3 (l) \\rightarrow \\text{NH}_3 (s)<\/p>\n\n\n\n<p>at <strong>-80\u00b0C<\/strong> and <strong>1 atm<\/strong>, the signs of thermodynamic parameters are:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u0394H (Enthalpy Change): Negative (-)<\/strong><br>Freezing is an <strong>exothermic<\/strong> process because heat is released when ammonia molecules transition from a higher-energy liquid state to a lower-energy solid state.<\/li>\n\n\n\n<li><strong>\u0394S (Entropy Change): Negative (-)<\/strong><br>Entropy decreases because a liquid has more molecular disorder than a solid. When ammonia freezes, its molecules become more ordered, leading to a reduction in entropy.<\/li>\n\n\n\n<li><strong>\u0394G (Gibbs Free Energy Change): Negative (-)<\/strong><br>Since ammonia normally freezes at <strong>-78\u00b0C<\/strong>, freezing at <strong>-80\u00b0C<\/strong> means the process occurs spontaneously. At temperatures lower than the normal freezing point, the solid phase is favored, making <strong>\u0394G negative<\/strong>.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Explanation<\/h3>\n\n\n\n<p>The freezing of ammonia at <strong>-80\u00b0C<\/strong> follows the principles of thermodynamics.<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Enthalpy Change (\u0394H):<\/strong><br>When a substance transitions from liquid to solid, intermolecular forces strengthen as molecules arrange into a fixed structure. This releases heat into the surroundings, making the process <strong>exothermic<\/strong>. Hence, <strong>\u0394H is negative<\/strong>.<\/li>\n\n\n\n<li><strong>Entropy Change (\u0394S):<\/strong><br>The second law of thermodynamics states that entropy, a measure of disorder, generally decreases when a substance solidifies. Liquids have more molecular motion and randomness than solids. As ammonia transitions from liquid to solid, its molecules become more ordered, reducing entropy, so <strong>\u0394S is negative<\/strong>.<\/li>\n\n\n\n<li><strong>Gibbs Free Energy Change (\u0394G):<\/strong><br>The Gibbs free energy equation is: \u0394G=\u0394H\u2212T\u0394S\u0394G = \u0394H &#8211; T\u0394S At temperatures <strong>below the freezing point (-78\u00b0C)<\/strong>, solid ammonia is the thermodynamically favored state. Since the system releases heat (<strong>\u0394H &lt; 0<\/strong>) and the decrease in entropy is more significant at low temperatures, the <strong>\u0394G value becomes negative<\/strong>, indicating a <strong>spontaneous process<\/strong>.<\/li>\n<\/ol>\n\n\n\n<p>Thus, at <strong>-80\u00b0C<\/strong>, ammonia spontaneously freezes because <strong>\u0394G &lt; 0<\/strong>, confirming that the process occurs naturally without external energy input.<\/p>\n\n\n\n<p>Now, I will generate an image illustrating this phase transition.<\/p>\n\n\n\n<p>Here is the scientific illustration showing the phase transition of ammonia from liquid to solid at -80\u00b0C, including thermodynamic properties like enthalpy (\u0394H &lt; 0), entropy (\u0394S &lt; 0), and Gibbs free energy (\u0394G &lt; 0). Let me know if you need any modifications!<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/03\/image-244.png\" alt=\"\" class=\"wp-image-196628\"\/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>The normal freezing point of ammonia is -78 degrees celsius. Predict the signs of Delta H, Delta S, and Delta G for ammonia when it freezes at -80 degrees celsius and 1 atm: NH3 (l) &#8212;> NH3 (s) The correct answer and explanation is: Answer: For the phase transition: NH3(l)\u2192NH3(s)\\text{NH}_3 (l) \\rightarrow \\text{NH}_3 (s) at [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-196627","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/196627","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=196627"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/196627\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=196627"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=196627"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=196627"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}