Why does splitting an atom create energy? And why is it so much energy?
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So there are two forces acting on those protons in the nucleus. There is an electrical force, and since protons and protons have the same charge, this repels them. There’s also a nuclear force which binds them together in the nucleus of an atom. The nuclear force acts over very short distances, so if you put in a bunch of energy, you can push those protons apart, and eventually the distance is long enough that the electrical force wins, and the protons to flying apart.
For small a small atom like helium, there’s only two protons, so the amount of energy of them flying apart is less than the energy it took to separate them. So if you split a helium atom, you would lose energy. For a bit atom like uranium, there are dozens of protons. Once you get them far enough apart, the electrical force takes over and you get more energy than you put in. So if you split a uranium atom, you gain energy.
Usually energy is just that – either heat or electrical voltage or something else. But when an atom is split a tiny amount of mass is converted into energy. Einstein’s E = m*c^2 tells us that mass is worth A LOT of energy and that’s exactly why splitting atoms creates so much energy
When you pop a balloon some energy is released.
When you pop an atom a bit more energy is released.
What “stored” the energy there for us to later “release”? The creation of the universe?
The strong force holds atoms together. It takes a different amount of energy to hold different atoms together. The energy required is highest at hydrogen, then it goes down until iron, and then back up at higher elements.
So when you go from hydrogen to helium, that smaller level of energy required is released. You can actually measure a small change in mass of the element, that mass is stored energy(E=MC^2).
It’s very similar to how chemical energy works. Chemical energy is just the weak force where different molecules require different energy to hold together. Typically the bigger the molecules, and the more carbons/hydrogens/nitrogens involved the more energy is required. The more energy required means more energy released.
Splitting atoms is a process called fission. During fission, we take a bunch of large atoms that are already radioactive and cram them into a confined space. Radioactive atoms constantly release energy in the form of particles in a process called radioactive decay. If you cram enough of these atoms together in one place, the particles that are being released will sometimes ram into the other atoms nucleus so hard that it causes them to split.
When the nucleus of an atom splits, something interesting happens. You get two new atoms (a collection of neutrons, protons, and electrons) plus some spare neutrons that go flying off to bump into other atoms, possibly splitting them. The interesting thing is that if you add up the weight of the two new atoms (called fission products) and the spare neutrons, the mass does not add up to that of the original atom.
The lost mass is around 0.1% of the original atom’s mass. This small amount of matter is literally converted from mass to energy. If you’ve ever heard of Einstein’s equation E = mc^(2), then you know that energy equals mass times the speed of light squared. The amount of energy you get from that mass-to-matter conversion follows this formula. In that formula:
Energy is Joules
Mass is kilograms
C is a physics constant for the speed of light in a vacuum, or 299792458 m/s.
So if you convert 1 gram (0.001 kg) of matter to energy, you’d get:
E = 0.001 × 299,792,458^(2)
Which works out to 89,875,518 Megajoules (8.9875517874×10^(13) Joules), or roughly 24,965,422 kWh. For a sense of perspective, a Tesla Model S P100D has a 100kWh battery. According to the EIA, the average US residential customer used 867 kWh per month in 2017. So almost 25 million kWh of energy is a LOT of energy, and that’s just in 1 tiny gram of matter.
In reality, we aren’t able to convert 100% of that energy into electricity. The conversion of heat to electricity in a typical nuclear power plant is just under 40%, so less than half of that is converted to energy. That’s still a lot of energy though.
As for why mass converts to energy at this specific rate, this is one of those fundamental questions that doesn’t have a more detailed answer than, “because that’s how it works.”
Imagine two balls attached to each other via very strong springs. If you pull on them slightly and let go, the springs will pull them back to their initial position.
If you however pull hard enough, the springs eventually snap and you suddenly recoil and fling the ball across the room. That kinetic energy is then being transferred to the other atoms ie. heat is generated.
This is more or less analogous to the limited range of the strong nuclear force. The only difference is that in nuclear fission the repulsive force does not come externally but rather from the Coloumb-Force between the components of the atom. You just have to snap the strings by pulling them far apart and that happens due to an atoms instability.
There is no such thing as a solid thing, everything is energy. Magnets are a good example of forces that make something feel solid when there isn’t something physical present (repulsion). What you are playing with is mass when you are dealing with atoms (energy packets). E=mc² is saying that you get the amount of energy that is equal to the mass of something multiplied by the velocity of the speed of light (big number) – that is assuming perfect conversion. Either way, it’s a boat load of energy and you’re undoing the binding that holds it together.
Splitting an atom causes others to split. The initial explosion using a conventional bomb is just to create enough force to split that initial atom. There are a lot of atoms in things. There are more molecules of water in a cup of water than there are cups of water on earth. So you’re getting a lot of atoms. But they’re small. The only real way to answer “why so much energy” is with an eli5 of “because that’s how much energy is in atoms”. It’s kind of like asking why 1+1=2, the fundamental properties of physics dictate how much gets stuffed in there and it happened to be quite a bit.
The energy creation comes from the escape of heat that can boil water which turns a turbine which creates electricity. As to what is actually happening to the atom, it isn’t creating energy it is being released.
There is a force that binds together the nuclei of an atom, if you break it into two smaller elements, a portion of the nuclear force is released as heat. That is called fission. Fusion is the opposite, you slam two atoms so hard that their nuclei merge. When you do that, you release at least one neutron and with it you release some nuclear force as heat.
In energy production you want this to happen to select groups of nuclei, so you use a ‘slow neutron’ or ‘fast neutron’ reactor. In a bomb you want all of the atoms to split at the same time, thereby releasing all of the forces at the same time.
There are four fundamental forces;
1. Gravity (the weakest by far)
2. The weak force
3. Electromagnetism
4. The strong nuclear force,
It’s actually not a huge amount of energy per atom and rather a whole lot of atoms releasing energy at the same time.
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