Why Do Molecules React

There are a number of factors that determine if molecules will react under a given set of conditions. We found a beautiful way of understanding this on the web.1 Think of a chemical reaction as a crime. In order for it to occur, there has to be both motive and opportunity. The motive is provided by thermodynamics. The products formed in the reaction need to be more stable than the reactants. There are two parts to this. Some reactions occur because of energetic factors the molecules formed in the reaction have stronger bonds (and are then at a lower energy) than the ones you started with. Other reactions go because of entropy, the final state of the system is more disordered than the initial state. This can happen if a number of smaller molecules are formed from fewer 

1 http //neon.cm.utexas.edu/academic/courses/ Spring2001/CH610B/Iverson/). 

How do molecules get over this barrier One important way is through collisions. The molecules have kinetic energy associated with their motion. The higher the temperature the faster they move. If you heat the mixture, a certain fraction of collisions will then involve enough energy to get the molecules over the hump. Essentially, 

FIGURE 3-3 Formation of an ester (shared electron approximation). 

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