Why does splitting an atom create energy? And why is it so much energy?


Why does splitting an atom create energy? And why is it so much energy?

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It doesn’t create energy. It releases the energy that is holding the particle together. That just happens to be a substantial amount of energy because holding particles so tightly is a lot of work.

The force that holds component protons and neutrons together – the strong nuclear force – is *very, uh,* strong.

It’s like a bunch of springs between all the components. When the atoms reconfigure, there are extra springs left over and the energy has to go somewhere. It takes the form of atomic kinetic – otherwise known as thermal – energy.

The energy is just bound into the fabric of the fuel and widely distributed, so you get high energy densities across the fuel source, without ridiculously volatile energy boundaries that are qualitatively hard to maintain.

This is an interesting question, because sometimes you get energy by pushing atoms together, *i.e.*, fusion, and sometime you get energy by splitting atoms apart, *i.e.*, fission.

There is a curve of what is called “binding energy per nucleon,” and it maxes out at ~~tin~~ *iron*, ~~which unsurprisingly has the most stable isotopes~~.

If you push two atoms together to make something smaller than tin, like 2 hydrogens to make a helium, you get A LOT of energy. If you split an atom apart to get two elements heavier than tin, you get some energy out. Still a lot, but not nearly as much.

Well, energy can’t be created or destroyed, but in this case, it gets released from one ‘form’ to another.

Imagine you are holding a heavy ball tied to a string, and you spin the ball above your head. You are adding energy into the system, but not creating it. You are sort of an atom.

What would happen if someone cut the string? The ball will fly off and smash into a window. The heavier the ball y, the worse the damage will be.

What if you had 245 heavy balls attached to strings, and each ball has a small blade attache to it? As long as only you are spinning them, it probably will be OK, though once in a while a ball mich get cut off and fly away. This is kind of what radioactive means, but very simplified.

And if you have hundreds, thousands, millions of people standing, each spinning 245 heavy, bladed balls above their head, things are bound to get messy! As long as each keeps a distance, it might be OK, though stray balls will fly off once in a while. But once you get enough people to smoosh together, their balls all fly off, setting off a chain reaction of flying, spinning, heavy, bladed balls everywhere!

This is a nuclear chain reaction.

It’s actually not a huge amount of energy per atom and rather a whole lot of atoms releasing energy at the same time.

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,

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.

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.

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.”

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.

What “stored” the energy there for us to later “release”? The creation of the universe?

When you pop a balloon some energy is released.
When you pop an atom a bit more energy is released.

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

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.

the answer is to do with einstein’s famous E=MC² equation. Energy = mass multiplied by the speed of light squared. The speed of light is a big number, so if you square it you get a damned big number.

When you split an atom into two smaller different atoms, the results weigh less than the original. the weight(mass) lost is converted into energy. Stunning loads of energy!

It takes a lot of energy to bind subatomic particles together to form an atom. When an atom becomes unstable, it can “split” into two smaller atoms. The subatomic particles separate to form two smaller atoms, but there’s some of that binding energy left over. That’s what gets released, and it’s very strong. Do this millions of times and ka-boom.

Particles which makes an atom have small range strong force that binds them together, and longer range weaker repelling force. So, this makes two ways to make energy of atom: 1).You either take an atom big to the point of small range force not spreading enough, you bombard it with neutrons and it splits, releasing more high velocity neutrons and recombining into more stable smaller atom, this leads to chain reaction with stable heat output or explosion(nuclear reactors and fission nuclear bombs). 2). You take small atoms containing extra neutron, heat them to the point of them crashing into each other so violently, that they break through the weak long range repelling force and get glued together by strong low range force. This creates tremendous (even compared to fore mentioned fission reaction) amount of energy, but the tricky part is getting to that temperature. It is achieved through separate fission reaction in thermonuclear bombs(like in tsar-bomb), high gravity fields(like inside stars), and fusion reactors for stable output are still being theoritised. Hopefully we can harness thermonuclear energy in safe way before the turn of the next century.
But if you are just curious, where that energy comes from, then the answer is mass. Standalone parts of atoms weight more than combined atom. Not by much, but since E=mc2, even miniscule amount of mass holds incredible amounts of energy.

Einstein realised that matter and energy are the same thing. A little bit of matter is the same as a lot of energy. When you split an atom, the two parts it splits into are slightly less than the whole you started with. The difference is released as a lot of energy.

when an atom splits, it blows off its electrons. so the two resulting atoms have a high positive charge and kind of act like a magnet. they will collect electrons from all around causing friction. and friction = heat and heat = energy

Atoms are made up of Protons, Neutrons and electrons. We can individually ‘weigh’ protons and neutrons to work out their mass (electrons are very low mass, so lets ignore them)

if you jam a bunch of protons and neutrons together to form an atom (lets say uranium 235, that has 92 protons and 143 neutrons, so a big heavy atom)

What should the atom weigh? 92 x proton weight + 143 x neutron weight right? its what you would expect, but it doesn’t, it weights less than this.

This mass difference is made up of the ‘nuclear binding energy’ (yeh, mass converting to energy and back, there is complicated science here too)

So now we crack that atom like a walnut, into two smaller atoms. Now weigh these, surely the total mass will be same the same as the original right? you would think, but the total mass is now a little Higher.

This is now where E=MC squared comes in (its actually change in energy = change in mass times the square of the speed of light) and because of the change in mass, there is a change of energy, and the excess energy gets released as heat/motion, usually through the reaction kicking out a seriously fast moving neutron or similar.