Final answer:
The greater the difference in energy between reactants and products, the more directional the reaction becomes. Exothermic reactions tend to proceed readily as they release energy, while endothermic reactions require energy input.
Step-by-step explanation:
The greater the difference in energy between reactants and products of a reaction, the more the overall reaction tends to go in one direction. In the context of potential energy diagrams, if the products have lower potential energy than the reactants, the reaction is said to be exothermic, and the energy change (ΔH) is negative. Conversely, if the products have higher potential energy, it is an endothermic reaction, and ΔH is positive. An exothermic reaction often proceeds more readily in the forward direction because it involves the release of energy to the surroundings, which can be seen as a path of least resistance compared to the energy input required for endothermic reactions.
An example of an exothermic reaction is the combustion of a hydrocarbon, like propane, in oxygen to produce carbon dioxide, water, and heat. For an endothermic reaction, consider the thermal decomposition of calcium carbonate into calcium oxide and carbon dioxide, which requires the input of heat.