In explaining why I haven’t been writing more Clear Science posts, I said the “activation energy” was high. That’s a scientific term. Imagine something has to go from start to finish. In the plot above, notice how finish is lower than start, meaning it has a lower energy. Things want to have a lower energy, so it’s natural to go from start to finish.
But there’s a problem: In order to get from start to finish, it has to go over a hump, which has higher energy than both start and finish. The energy required to go over this hump is called the activation energy. It’s like some extra energy required to get to an overall better (lower energy) state.