{"id":56,"date":"2017-10-23T14:10:38","date_gmt":"2017-10-23T14:10:38","guid":{"rendered":"http:\/\/chemdictionary.org\/?p=56"},"modified":"2017-11-14T12:24:36","modified_gmt":"2017-11-14T12:24:36","slug":"equilibrium-constant-kp","status":"publish","type":"post","link":"https:\/\/chemdictionary.org\/equilibrium-constant-kp\/","title":{"rendered":"Equilibrium Constant Kp"},"content":{"rendered":"<h2><span style=\"color: #000000\">Equilibrium Constant Kp Definition<\/span><\/h2>\n<p>When a reaction is at equilibrium, the forward and reverse reaction rate are same. The concentration of the reactants and products stay constant at equilibrium, even though the forward and backward reactions are still occurring.<\/p>\n<p>When one or more of the reactants or products are gas in any equilibrium reaction, the equilibrium constant can be expressed in terms of partial pressure.\u00a0Equilibrium constant expression in terms of partial pressure is designated as K<sub>p<\/sub>.<\/p>\n<p>Equilibrium constant Kp is equal to the partial pressure of products divided by partial pressure of reactants and the partial pressure are raised with some power which is equal to the coefficient of the substance in balanced equation.<\/p>\n<h2><span style=\"color: #000000\">Equilibrium constant expression in terms of partial pressures<\/span><\/h2>\n<p>Let us consider a general gas phase equilibrium reaction where a moles of A molecule reacts with b moles of B molecule to form c moles of C molecule and d moles of D molecule.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-99\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-6.png\" alt=\"\" width=\"269\" height=\"51\" title=\"\"><\/p>\n<p>According to equilibrium law the equilibrium constant K<sub>p<\/sub>\u00a0can be written as<\/p>\n<p><img loading=\"lazy\" class=\"alignnone wp-image-159\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-5.png\" alt=\"\" width=\"115\" height=\"71\" title=\"\"><img loading=\"lazy\" class=\"alignnone  wp-image-163\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-10.png\" alt=\"\" width=\"91\" height=\"33\" title=\"\"><\/p>\n<p>Here P<sub>A\u00a0<\/sub>,\u00a0P<sub>B<\/sub>,\u00a0P<sub>C\u00a0<\/sub>and P<sub>D\u00a0<\/sub>are the partial pressure of gas A, B, C and D respectively. And\u00a0K<sub>p <\/sub>is equilibrium constant and subscript <span style=\"font-size: 13.3333px;line-height: 20px\">p<\/span>\u00a0refers to partial pressure. Partial pressures are expressed in atmosphere.<\/p>\n<div class=\"paragraph\">\n<h3 class=\"paragraph\">The important points to be remembered to write the expression of\u00a0K<sub>p<\/sub><\/h3>\n<ul>\n<li>In equilibrium equations, even though the both sided arrows (\u21cc) are used we consider left sided elements as reactants and\u00a0right sided elements as products.<\/li>\n<li>The products are on the top\u00a0in the expression (the numerator).<\/li>\n<li>The reactants stays on the bottom\u00a0(the denominator).<\/li>\n<li>The partial pressure of the products and reactants are always raised to the power which is equal to the numerical coefficient of the respective substance in the balanced chemical equation.<\/li>\n<li>For any heterogeneous system the partial pressure of pure solids and liquids are not included in the equilibrium constant expression.<\/li>\n<\/ul>\n<\/div>\n<h2>K<sub>p\u00a0<\/sub>in homogeneous gaseous equilibria<\/h2>\n<p>A homogeneous gaseous equilibrium is one in which all the reactants and products are in gas phase. A good example of homogeneous gaseous equilibrium is the formation of ammonia through the Haber Process.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-95\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-3.png\" alt=\"\" width=\"251\" height=\"48\" title=\"\"><\/p>\n<p>The K<sub>p\u00a0<\/sub>expression for this equilibrium reaction is<\/p>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-96\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-4.png\" alt=\"\" width=\"155\" height=\"82\" title=\"\"><\/p>\n<h2>K<sub>p\u00a0<\/sub>in heterogeneous equilibria<\/h2>\n<p>A heterogeneous equilibrium is one where reactants and products are not in same phase. For heterogeneous equilibrium the partial pressure of pure solids and liquids are not included in the equilibrium constant expression. As for example the heating of calcium carbonate in a closed vessel to form calcium oxide and carbon dioxide.<\/p>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-93\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-1.png\" alt=\"\" width=\"268\" height=\"47\" title=\"\"><\/p>\n<p>Here only carbon dioxide is in gas phase. The equilibrium constant for this reaction (by excluding any terms for solid) is<\/p>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-94\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/kp-2.png\" alt=\"\" width=\"99\" height=\"48\" title=\"\"><\/p>\n<h2>Relationship between\u00a0K<sub>p<\/sub>\u00a0and\u00a0K<sub>C<\/sub><\/h2>\n<p>Assuming that all the gases in equilibrium reaction obey the ideal gas equation, the partial pressure (p) of a gas is<\/p>\n<p>PV = nRT<\/p>\n<p>Divide both sides by V,<\/p>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-101\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-7.png\" alt=\"\" width=\"109\" height=\"57\" title=\"\"><\/p>\n<p>Here n\/V is the molar concentration. Thus the partial pressures of individual gases A, B, C and D are:<\/p>\n<p><strong>P<sub>A<\/sub> = [A]RT;\u00a0<\/strong><strong>P<sub>B<\/sub>\u00a0= [B]RT;\u00a0<\/strong><strong>P<sub>C<\/sub> = [C]RT;\u00a0<\/strong><strong>P<sub>D<\/sub> = [D]RT<\/strong><\/p>\n<p>Substituting these value in equilibrium constant expression equation 1, we have<\/p>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-160\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-8.png\" alt=\"\" width=\"260\" height=\"77\" title=\"\"><\/p>\n<p><img loading=\"lazy\" class=\"alignnone size-full wp-image-161\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2017\/10\/Kp-9.png\" alt=\"\" width=\"266\" height=\"75\" title=\"\"><\/p>\n<p><strong>\u00a0 \u00a0 K<\/strong><strong><sub>P<\/sub><\/strong><strong> = K<sub>C<\/sub> (RT)<sup>(c+d)-(a+b)<\/sup><\/strong><\/p>\n<p><strong>\u00a0 \u00a0 K<\/strong><strong><sub>P<\/sub><\/strong><strong> = K<sub>C<\/sub> (RT)<sup>\u2206n \u00a0 <\/sup><\/strong>&#8230;&#8230;&#8230;&#8230;..(2)<\/p>\n<p>where\u00a0\u2206n = (c+d) &#8211; (a+b), the difference in the sums of the coefficients for the gaseous products and reactants.<\/p>\n<p>From the expression (2) it is clear that when\u00a0 \u00a0 \u2206n=0,\u00a0K<sub>p\u00a0<\/sub>= K<sub>c<\/sub>.<\/p>\n<h2>Summary<\/h2>\n<ul>\n<li>Equilibrium constant Kp is equal to the partial pressure of products divided by partial pressure of reactants and the partial pressure are raised with some power which is equal to the coefficient of the substance in balanced equation.<\/li>\n<li>For any heterogeneous system the partial pressure of pure solids and liquids are not included in the equilibrium constant expression.<\/li>\n<li><strong>K<\/strong><strong><sub>P<\/sub><\/strong><strong> = K<sub>C<\/sub> (RT)<sup>\u2206n<\/sup><\/strong><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Equilibrium Constant Kp Definition When a reaction is at equilibrium, the forward and reverse reaction rate are same. The concentration of the reactants and products stay constant at equilibrium, even though the forward and backward reactions are still occurring. When one or more of the reactants or products are gas in any equilibrium reaction, the &#8230; <a title=\"Equilibrium Constant Kp\" class=\"read-more\" href=\"https:\/\/chemdictionary.org\/equilibrium-constant-kp\/\" aria-label=\"More on Equilibrium Constant Kp\">Read more<\/a><\/p>\n","protected":false},"author":5,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"rating_form_position":"","rating_results_position":"","mr_structured_data_type":""},"categories":[3],"tags":[15],"multi-rating":{"mr_rating_results":[{"adjusted_star_result":4.41,"star_result":4.41,"total_max_option_value":5,"adjusted_score_result":4.41,"score_result":4.41,"percentage_result":88.18,"adjusted_percentage_result":88.18,"count":22,"post_id":56}]},"_links":{"self":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/56"}],"collection":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/comments?post=56"}],"version-history":[{"count":0,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/56\/revisions"}],"wp:attachment":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/media?parent=56"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/categories?post=56"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/tags?post=56"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}