Hi
@billy201x -
Excellent question! I think it may help to step back and clarify the terminology a little bit. "High-energy" and "low-energy" can be confusing terms sometimes because we have to think about "high" and "low"
relative to something. In general, thermodynamics tells us that energy likes to be distributed throughout the environment, so something that "contains" a high amount of energy is going to be relatively unstable. You can use an analogy with gravitational potential energy here -- you certainly
can lift a heavy object above your head, giving it high gravitational PE, but that's not the most stable situation. Therefore,
reduced energy (relative to the surroundings) =
more stable. Based on your initial post, it seems like you have that intuition down, but it never hurts to review it.
The details of the underlying physics go beyond the MCAT, but covalent bonds form in the first place because it is energetically favorable for them to do so. Thus, a molecule of methane (CH4) is lower-energy and more stable than its components in isolation. Therefore, if you want to break those bonds, you will have to invest energy. The more stable the bond, the more energy you will have to invest to break it. This is usually referred to as the
bond dissociation energy, and if you just see the term "bond energy", that is often what they're referring to. So
lower-energy bonds have less energy than their non-bonded components, and are more stable, so
more energy has to be put in to
break the bonds.
Another way of thinking about this is that "low-energy" bonds refers to the energy that is tied up, so to speak, in the bond. To break these bonds, you have to invest a lot of energy from the outside, which is the bond dissociation energy. The analogy with gravitational potential energy might help here as well. Imagine that we have five books on a shelf, and one falls to the floor. The book that fell is now "low energy" compared to the books on the shelf, and we'd have to invest energy to get it back up there. The further it falls, the "lower energy" it becomes, and the more energy we have to use to get it back up. For molecules, when bonds are formed, that's like the book that fell to the floor, and breaking the bonds is like putting the book back on the shelf.
Hope this is helpful, & best of luck studying!