CHEM 112 Study Guide - Midterm Guide: Arrhenius Equation, Elementary Reaction, Threshold Energy

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10 Sep 2016
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Rates of chemical reactions define behavior, reactivity, properties, and application. Collisions between molecules will lead to chemical reactions: not all collisions will necessarily lead to a chemical reaction, collision frequency, orientation, and chemical reactivity determine whether or not a collision will cause a reaction. Heat, catalysts, concentration, and phase will influence the reaction rate: rate # effective collisions/time, rate [x]; rate = k[x, k = the proportionality or rate constant. Only molecules with sufficient (activation or threshold) energy (denoted as ea) can react. Intermediates occur during the steps that together will form an overall reaction. For example, consider 2no(g) + o2(g) 2no. The steps may be: no + no n2o2, n2o2 + o2 2no2. Here, n2o2 is the intermediate: the highest peak in the graph denotes which step in the reaction is the rate-limiting step, or the slowest step in the reaction. If e is positive, the reaction is endothermic. If e is negative, the reaction is exothermic.