Question #eb856

A potential energy diagram shows you the key thermodynamic aspects of a chemical reaction, as well as a few other tidbits.

Overall, looking at the shape of the diagram, you can tell if the reaction is exothermic or endothermic. Remember that exothermic reactions release energy from the system (reactants) to the environment and endothermic requires an input of energy into the system from the environment.

The x-axis denotes the progress of the reaction: at the origin, it is before any reaction takes place. In the middle, it is during the reaction. at the end, it is after the reaction has completed
The y-axis denotes energy. Up is higher energy (more positive, more unstable) and lower is lower energy (more negative, more stable)

So, if your reactants are at a higher energy level (y-value) than your products, then you have an exothermic reaction, since there was a net loss in energy after the reaction took place

Another thing you could look at is the height of the peak, which shows you the activation energy required to allow the reaction to proceed. This is useful, for example, when comparing catalyzed and uncatalyzed reactions. In a catalyzed reaction, you will notice that the activation energy is much lower.

Note that a potential energy diagram only gives you direct information about the thermodynamics (how favorable) of the reaction, and not the kinetics (how fast). However, we can infer that reactions with a large activation energy will be slower than a reaction with a small activation energy given the same temperature, pressure, and other conditions.