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A pedantic point, but hydrocarbons don’t actually “store energy”. The energy from the combustion actually comes from the oxygen! We just don’t think of it as th
by lovecg 5y ago
A pedantic point, but hydrocarbons don’t actually “store energy”. The energy from the combustion actually comes from the oxygen! We just don’t think of it as the “fuel” since it’s so abundant.
A better intuition is this: plants, etc. used energy to create two products, oxygen (which went into the atmosphere) and hydrocarbons (buried in the ground). When we recombine them and add heat, we reconfigure some bonds and release energy in the oxygen bond. The hydrocarbons act as a “sponge” for the oxygen atoms, and the denser the sponge the more energy we can release.
If it was the oxygen buried underground we would probably call it “fuel”!
- Robotbeat 5y agoWhether you consider the energy stored in the oxygen or the hydrocarbon doesn’t particularly matter. The energy is in them being split apart. I read a proposal to send an aircraft to Titan and bring along oxygen as the energy source to burn with the methane in the atmosphere. (It works… sort of. In a methane and oxygen stoichiometric reaction, the oxygen is 4/5ths the mass so it’s not nearly as good of a deal as it is on Earth.)
- mr_toad 5y agoSince Titan’s surface is mostly water ice you’d think it would be easier to use electrolysis to generate oxygen locally.
- blendergeek 5y ago> Whether you consider the energy stored in the oxygen or the hydrocarbon doesn’t particularly matter. It truly doesn't matter which one you consider it to be, given that both are technically incorrect. > The energy is in them being split apart. This is a common misconception (likely) perpetuated by highschool chemistry textbooks. The energy is actually release by the combination of oxygen with hydrogen and carbon. Let me explain. It takes energy to break chemical bonds. Some bonds take more energy to break, others take less. When a bond is created, an amount of energey (roughly) equal to the energy require to create the bond is released. Here I will demonstrate the combustion of a simple hydrocarbon: CH4 + 2 O2 -> CO2 + 2 H2O When this reaction takes place, there is not energy "stored" in either the Carbon-Hydrogen bonds or the Oxygen-Oxygen bonds that is "given off". Rather, energy is actually required to break the bonds. It goes something like this: CH4 + 2 O2 + (a little bit of energy) -> CO2 + 2 H2O + (a lot of energy). Making hydrocarbons (or hydrogen from water) is an energy intensive process because breaking the bonds in CO2 and H2O requires a lot of energy.
- Robotbeat 5y agoYes, I didn't say the energy is stored in the bonds or is released by breaking bonds. I was referring to the fact that photosynthesis (or electrolysis) is used to separate the oxygen from the carbon/hydrogen in H2O or CO2. That's where the energy is stored (in the separation of the fuel from the oxygen).
- lovecg 5y agoYeah this is correct and I was oversimplifying. Though that begs the question of how that equation balances out - where does (a lot of energy) comes from? The products on the right side sit at a lower energy level (they hold together “tighter”) overall. On the left, O2 needs less energy to break up while CH4 needs more, so in that sense the energy “comes” from O2 being easier to break apart. Conceptually I imagine these as a bunch of magnets with the two “magnets” in O2 held at a larger gap (so easier to take apart). With a jolt, things reconfigure and snap into a tighter pattern, and there’s an overall energy release.