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General Chemistry Principles, Patterns, and Applications, 2011

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The<br />

diagram shows how the energy of this system varies as the reaction proceeds from reactants to<br />

products. Note the initial increase in energy required to form the activated complex.<br />

Part (a) in Figure 14.22 "Differentiating between " illustrates the general situation in which the products<br />

have a lower potential energy than the reactants. In contrast, part (b) in Figure 14.22 "Differentiating<br />

between " illustrates the case in which the products have a higher potential energy than the reactants, so<br />

the overall reaction requires an input of energy; that is, it is energetically uphill, <strong>and</strong> ΔE > 0. Although the<br />

energy changes that result from a reaction can be positive, negative, or even zero, in all cases an energy<br />

barrier must be overcome before a reaction can occur. This means that the activation energy is always<br />

positive.<br />

Figure 14.22 Differentiating between Ea <strong>and</strong> ΔE<br />

The<br />

potential energy diagrams for a reaction with (a) ΔE < 0 <strong>and</strong> (b) ΔE > 0 illustrate the change in the<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

1322

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