How Activation Energies Affect Reaction Rates

A FIGURE 15.15 Hill analogy for activation energy There are several ways to get these boulders over the hill as fast as possible, (a) One way is simply to push them harder—this is analogous to an increase in temperature for a chemical reaction, (b) Another way is to find a path that goes around the hill—this is analogous to the role of a catalyst for a chemical reaction. 

A catalyst does not change the position of equilibrium, only how fast equilibrium is reached. 

Upper-atmospheric ozone forms a shield against harmful ultraviolet light that would otherwise enter Earth s atmosphere. See the Chemistry in the Environment box in Chapter 6. 

For rolling boulders, the higher the hill is, the harder it will be to get the boulders over the hill, and the fewer the number of boulders that make it over the hill in a given period of time. Similarly, for chemical reactions, the higher the activation energy, the fewer the number of reactant molecules that make it over the barrier, and the slower the reaction rate. In general  

At a given temperature, the higher the activation energy for a chemical 

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