What was Sisyphus’s punishment?
Sisyphus was a mythological being who had been a very evil king. As a punishment, he was supposed to roll a large stone up to the top of a long hill. A spell had been placed on the stone so that it would roll back down before reaching the top, so the task could never be completed. Sisyphus was condemned to an eternity of trying to get to the top of the hill, but never succeeding.
Potential Energy Diagrams
The energy changes that occur during a chemical reaction can be shown in a diagram called a potential energy diagram, or sometimes called a reaction progress curve. A potential energy diagram shows the change in potential energy of a system as reactants are converted into products. Figure below shows basic potential energy diagrams for an endothermic (A) and an exothermic (B) reaction. Recall that the enthalpy change
The activation energy for a reaction is illustrated in the potential energy diagram by the height of the hill between the reactants and the products. For this reason, the activation energy of a reaction is sometimes referred to as the activation energy barrier. Reacting particles must have enough energy so that when they collide they can overcome that barrier (see Figure below).
- Potential energy diagrams for endothermic and exothermic reactions are described.
- Diagrams of activation energy and reaction progress are given.
- In an endothermic reaction, is the potential energy of the products higher or lower that the potential energy of the reactants?
- In an exothermic reaction, is the potential energy of the products higher or lower that the potential energy of the reactants?
- What does activation energy tell us?