Original post: Friday, May 18th, 2007<\/p>\n
The study of kinetics is to find out the things that affect how fast reactions occur and then ultimately to explain the actual mechanics of the process (what actually happens and in which order)
\nOn the basic level, simply observation shows us that changing the concentration of reactants affects the rate of formation of products (or disappearance of reactants) – the question is, \u201cwhat exactly is the relationship between reactant concentration and rate?\u201d
\nMathematically speaking there are only three logical possibilities:
\n1. There is no relationship
\n2. There is a linear relationship
\n3. There is a non-linear relationship
\nAll three possibilities can be covered by one generic equation, called the rate equation:
\nFor a one component (A) system\u2026
\nRate = k [A]^x
\nfor a two component (A + C) system
\nRate = k[A]^x[C]^y
\nAt the very beginning of a reaction the initial rate can be found (or a close approximation) by experiment. We also know the concentration of the reactants at this time (we choose them), so if two experiments are carried out on a one component system we have two unknowns (k and x) and two equations – simultaneous equations that can then be solved for k and x
\nFor two component systems (A+C) things get a little more complicated – but only a little. Two experiments must now be carried out, keeping the concentration of one of the reactants constant (say, C). The second equation can then be written as:
\nRate = constant [A]^x
\nwhere the constant is (k[C]^y)
\nand once again you have two simultaneous equations with two unknowns. The constant doesn\u2019t concern us at this time so you just solve for x.
\nNow you carry out two reactions keeping [A] constant when the rate equation can be simplified to:
\nRate = constant[C]^y
\nnow solve for y
\nNow you can choose any of the experimental results to substitute for x and y to find k (the rate constant)
\nWhy do we go through all of this?
\nThe answer lies in the fact that the orders of reaction x and y give us hints about likely mechanisms as they show the molecularity (number of particles ) involved in the rate determining step (slowest step) of the mechanism (and possibly any prior equilibria)
\nFor example, if the rate equation comes out to be
\nRate = k[A]^2[C]^0
\nThis tells us that the rate determining step (slowest) does not involve C in any way and probably involves a step with two particles of A..
\npossibly:
\n2A \u2013> A2 (slow step)
\nConclusion:
\nKinetics is a wholly experimental branch of chemistry that seeks answers to what actually is happening during the course of a reaction. It does so by \u2019solving\u2019 the rate equation – a general equation that can be adapted for 1, 2 or 3 component systems.
\nThe orders (x and y) give clues as to the mechanism of the reaction.
\nOnce the orders of reaction with respect to the individual components of the reaction are found, further investigations at different temperatures can be carried out to find the activation energy of the reaction using the Arrhenius equation.
\nAdvantages? All the calculations in exam questions involve VERY simple maths and once the concepts are grasped it\u2019s easy marks.<\/p>\n","protected":false},"excerpt":{"rendered":"
Original post: Friday, May 18th, 2007 The study of kinetics is to find out the things that affect how fast reactions occur and then ultimately to explain the actual mechanics of the process (what actually happens and in which order) On the basic level, simply observation shows us that changing the concentration of reactants affects […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[56,81,82,84],"class_list":["post-18","post","type-post","status-publish","format-standard","hentry","category-physical","tag-kinetics","tag-rate-constant","tag-rate-equation","tag-rates-of-reaction"],"_links":{"self":[{"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/posts\/18","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/comments?post=18"}],"version-history":[{"count":0,"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/posts\/18\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/media?parent=18"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/categories?post=18"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ibchem.com\/blog\/wp-json\/wp\/v2\/tags?post=18"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}