The Let's Play Archive

SpaceChem (2013 Tournament)

by Wild M

Part 19: The Chem in SpaceChem - Round 6

The Chem in SpaceChem, Round 6

Leylite posted:

If I were to ask for more, I'd like to see some numbers on whether the reactions are exothermic or endothermic, and how much energy is released/required.
Alright, I can do that. But I’ll have to explain a few things first.

Reaction energy

Every chemical reaction is either exothermic or endothermic. Exothermic reactions have a net release of energy, while endothermic reactions use up energy. ‘Therm’ refers to heat, but these words are also used when another form of energy, such as light, is released or used. Chemical energy is stored in the chemical bonds, so to find out if a reaction is exo- or endo-, all you need to do is compare the total chemical energy in the reactants with the total chemical energy in the products. For common molecules, the chemical energy (standard enthalpy of formation) has often been determined practically and I can easily calculate the reaction energy. For less common, unstable, and fictional molecules, it is possible to theoretically predict those values, but that is quite difficult and I won’t be doing that. Instead, I’ll use my chemical instincts to guess if such a reaction would be exothermic or endothermic.

By the way, exothermic and endothermic doesn’t say anything about how hard it is to make a reaction ‘go’. That has to do with activation energy, reaction kinetics, reaction equilibrium, and some other thermodynamics stuff. Feinne, you explained some of this stuff already, but you seem to imply that exo-/endothermic is related to reaction kinetics. I disagree, kinetics simply show how fast a reaction will go. There are kinetically favorable endothermic reactions and kinetically unfavorable exothermic ones. Kinetics are separate from both activation energy and reaction energy.


12: Jailbreak
Input molecules: Iron(II) oxide, Hydrogen
Output molecules: Iron(II) oxide

Net reaction: None. But there’s still interesting stuff going on in the reactor.

Wüstite, Iron(II) oxide, FeO
Melting point: 1377 °C, 2511 °F
Boiling point: 3414 °C, 6177 °F
Molecular mass: 71.84u
Density: 5.76 kg/L

Wüstite is one of the oxides of iron. It is not regular rust, which is mostly Fe2O3. It looks like a black powder. Wüstite makes up about 9% of earth’s mantle and is used as a pigment in tattoos and cosmetics.

FeO is also the first example of a salt I get to talk about. Salts are not made of molecules. Instead, they are made of ions, charged atoms. The (II) in the name means iron has a charge of 2+ here. Oxide always has a charge of 2–. The unit of charge is the electric charge in one electron. The ions are kept together by electrostatic forces in a large crystal structure. In the case of FeO, the crystals are cubic, similar to table salt. A single crystal consists of gazillions of ions, all bound together. FeO molecules do not exist, and ‘FeO’ is nothing more than an empirical formula that shows the Fe : O ratio is 1 : 1. To melt a salt, you need to overcome the strong electrostatic forces holding the crystal together, so salts typically have high melting points.

Hydrogen, H2
Melting point: -259 °C, -434 °F
Boiling point: -253 °C, -423 °F
Molecular mass: 2.016u
Density: 0.09 g/L

Hydrogen is the most common element in the universe, as about 90% of all atoms are hydrogen.

On earth, it forms the H2 molecule, which is the lightest we have. It is a non-toxic but highly combustible gas, that produces nothing but water when it burns. Helium and hydrogen are both light enough to actually escape from earth’s gravity, and the tiny molecules can also slowly leak through most containers. Hydrogen is famous from the Hindenburg disaster, the airship filled with hydrogen that caught fire. However, nowadays scientists believe the fire was caused by the frame or skin of the ship, and that the hydrogen didn’t have that much to do with it. Still, hydrogen balloons aren’t used any more.

Hydrogen gas has gained some popularity as a fuel, but the problem is that there’s barely any natural hydrogen gas on earth. You first have to use another kind of energy to produce the gas. Another challenge is to find ways to safely transport the stuff. The gas is also used for a lot of different purposes in chemical industries, and the element is used for nuclear fusion.

Interestingly, when hydrogen is put under enormous pressures (such as at the center of Jupiter), it starts behaving like a metal. It’s not yet possible to recreate this behavior on earth, but it would have useful applications, for instance as a superconductor.

Making hydrogen is not very difficult: just react a base metal with an acid, or electrolyze water. Industrially, it can also be produced from hydrocarbons.

Feasibility of the reaction
Feasibility: low, assuming that fusion and fission is required.

Chemically, nothing much is happening. Let’s talk about nuclear fission and fusion instead. Of course, when you think of nuclear reactions, you think of energy production and atomic bombs. Nuclear reactions can release lots of energy. That's true for both fusion and fission. Those processes are opposite, how is that possible?

Well, when you bring positively charged protons (one of the two building blocks of atomic nuclei) together they will strongly repel each other electromagnetically. Only at very short distances, attractive nuclear forces will become stronger. There’s a lot of energy involved in keeping them together. This energy is actually stored in the form of mass, according to Einstein’s E=mc2. The mass of the nucleus divided by the number of particles in the nucleus (‘nucleons’) is a good indication of the stored energy. The higher the mass, the more energy is stored. When you go from hydrogen to larger and larger atoms, the mass per nucleon keeps decreasing.

For instance, hydrogen-1 (The one means there’s just one nucleon. There’s also hydrogen-2 which has an additional neutron.) has a mass/nucleon of 1.00783u while helium-4 has a mass/nucleon of 1.00065. This means, 0.00718u per molecule of hydrogen or 7.18g for each kilogram is released as energy when you fuse hydrogen-1 into helium-4. That’s 645 TJ or 154 kilotons TNT of energy per kilogram hydrogen. Phenomenal cosmic powers… itty-bitty amount of matter.

Anyway, when you go to larger atoms, the mass per nucleon keeps decreasing, until you hit iron. It has the lowest mass per nucleon of all elements, and beyond that the ratio starts increasing. Apparently, the nuclei are getting so big that repulsive forces get significant again. This means that it costs energy to fuse to something beyond iron, but when you split such a heavy element, energy is released.

Fusion energy comes from fusing very light elements, fission energy comes from splitting very heavy elements.

Stars are giant fusion reactors, but they will stop when they reach iron. All elements up to iron were made in stars, while everything heavier than that was made in supernovae, which have enough energy to force heavier fusion.

Back to the problem at hand: using fusion and fission in order to create elements. Because of the enormous energies involved, it doesn’t seem feasible at all to make any significant amount of new elements this way. Either it costs more energy than we could ever generate, or we get an enormous surplus which will cause unprecedented global warming. We could theoretically get to a finicky equilibrium, but the challenges involved in making that work would be incredible, and any accident would be enormous.

Then again, fusion is practically a limitless source of energy. If, far in the future, we are able to control fission and fusion precisely, we commonly use nuclear reactors to power our starships and planetary colonies, there’s probably some redundancy built in. In that case I could imagine a very powerful and rich organization requesting to use some of the extra reactors to create rare elements. Radioactive waste and waste energy can just be dumped in space or on a lifeless planet.

In other words, the only society in which this could possibly be feasible is one similar to the SpaceChem background story.

Reaction energy: Endothermic
That’s strange. Why would a reaction in which there’s no net change be endothermic? Well… when you do any nuclear reaction, some small particles such as neutrinos will fly out. It costs some energy to create these particles, and it’s nearly impossible to catch them. So it will cost a little bit of energy to keep this back-and-forth reaction going.


13: Crossover Filter
Input molecules: Nitrous Oxide, Carbon Dioxide
Output molecules: Carbon Dioxide, Nitrous Oxide

Net reaction: none.
I talked about Carbon Dioxide in my previous post, so I’ll skip it this time.

Laughing gas, Nitrous oxide, dinitrogen monoxide, N2O
Melting point: -91 °C, -132 °F
Boiling point: -88 °C, -127 °F
Molecular mass: 44.01u
Density: 1.977 g/L

N2O isn’t called laughing gas for nothing. When inhaling it, it has an euphoric and anesthetic effect. While this effect was known since the 18th century, it was Horace Wells who first used it as a dentistry anesthetic in 1844.
Other than that, it is used as a spray propellant for whipped cream (because it dissolves well in the cream’s fat, and doesn’t affect the taste), and as an oxidizer in rocketry and car racing (‘nitrous’). At high temperatures (above 1300 °C/ 2370 °F), with a catalyst it will decompose into nitrogen and oxygen gas, releasing lots of energy in the process. This way, it can be used as a monopropellant in rockets.

Nitrous oxide is usually prepared from carefully heating ammonium nitrate. This reaction is tricky, because at the temperature at which N2O is formed, ammonium nitrate is explosive. In nature, soil and ocean bacteria turn nitrogen compounds into nitrous oxide.

In the atmosphere, it acts as a very strong greenhouse gas, 310 times as potent as CO2. Moreover, it removes ozone from the ozone layer.

Feasibility of the reaction
Feasibility: high

Quantum tunneling is a real thing with real uses. To understand it, we need to dive into the complex subject of quantum mechanics. I’ll try to keep things simple. Basically, quantum mechanics describe the position and momentum of any particle as a probability. For instance, there is usually a high probability that an electron stays close to its atom and a very low probability that it escapes or falls into the nucleus.

Now, imagine you had a tiny tiny insulator, which we call a tunnel junction. It is thick enough so an electron couldn’t possibly have enough energy to ‘drill’ through it. Quantum mechanically, the probability of the electron being at a position drops dramatically in and beyond the insulator. However, the probability follows a sort of curve and does not drop to zero immediately. Even though classically, the electron doesn’t have enough energy to get to the other side, quantum mechanically there is still a positive probability of this happening. And it does actually happen, by ‘borrowing’ energy from the environment. This is theoretically possible at all scales, but the probability of tunneling is negligible beyond a distance of a few nanometers. Management is not responsible for damage caused by attempts to tunnel macroscopic objects through walls or windows.

In nature, it is an important part in making nuclear fusion and regular radioactivity work (particles actually tunnel into or out of an atom’s nucleus). Apparently, spontaneous mutations in DNA, which both cause evolution and cancer, could be caused by tunneling effects as well.

In engineering, quantum tunneling plays a role in a certain kind of diode, in certain solar cells, and in the future it might become important in electronic devices such as computers and electronic displays. I think the most interesting application of quantum tunneling is the Scanning Tunneling Microscope. This device uses a tiny, very sharp tip. A voltage is applied between the tip and the object to be scanned. Then the tip is brought in ‘tunneling range’ of the object (tenths of nanometers). When it’s right on top of an atom, electrons from the atom will easily tunnel to the tip. This way, the STM can image an object at the atomic level. Using the device in another way actually allows moving single atoms around. In this picture, the Center for NanoScience moved molecules around to draw a tiny version of their logo. I guess an STM is kind of like a SpaceChem waldo?

Anyway, tunneling is common and with the right equipment it’s easy to manipulate. This ‘reaction’ is definitely feasible.

Reaction energy: Neutral
You’re not changing anything, and tunneling temporarily ‘borrows’ energy from its environment so this one is neutral.


Challenge 6: Pertetroxide Synthesis
Input molecules: Methane tetraol
Output molecules: Methyl pertretroxide

Net reaction: C(OH)4 --> CH3O4H
We’re talking about isomers here, so the only way I can show a net reaction is by not using the molecular formulas but these semi-structural ones. It doesn’t matter much.
By the way, there’s a typo in the product ‘formula’, it says 6 O’s instead of 4.

Orthocarbonic acid, Methane tetraol, C(OH)4
Melting point, Boiling point, Density: No clue.
Molecular mass: 80.04u

Wikipedia posted:

Orthocarbonic acid or methanetetraol is the name given to a hypothetical compound with the chemical formula H4CO4 or C(OH)4. The compound is believed to be highly unstable, decomposing spontaneously into carbonic acid monohydrate.
Well, that settles that. They do note that larger compounds based on this CO4 group are stable. Methanetriol is not stable either, but methanediol is. If methanetetraol could be formed, it would be so unstable that in practice it would act like its decomposition product carbonic acid.

Methyl pertretoxide, methyl tetraoxidane, CH3O4H
Melting point, Boiling point, Density: No clue.
Molecular mass: 80.04u

This one is certainly fictional, and I can’t find any information on it. So I’ll take a look at some related compounds.

First, there’s methylhydroperoxide, CH3O2H. Like all peroxides (compounds with a single O-O bond), it is quite reactive. However, it is actually stable enough to experiment on. [1] reports that during their experiments, only 2 spontaneous explosions occurred. So no worries. This stuff reacts with a lot of things and also decomposes when heated enough.

The compound H-O-O-O-H is called trioxidane and is a rare and unstable molecule, decomposing into water and singlet oxygen in minutes. (Singlet oxygen is very similar to normal molecular oxygen, but it is in a quantum mechanically ‘excited’ state, making it much more reactive to organic matter. It can be dangerous when released ‘into the wild’.) I also found just a few sources on H-O-O-O-O-H. It seems to be a very unstable combination of two HO2 radicals, which have an unpaired electron, making them extremely reactive. One source states it decomposes at temperatures above -115 °C / -175 °F.

Methyl pertretoxide doesn’t exist, and if it did, it would be extremely unstable and probably explosively so.

Feasibility of the reaction
Feasibility: low
Reacting a fictional molecule predicted to be very unstable into a fictional molecule predicted to be explosively unstable… what could possibly go wrong?

This is just not going to happen.

Reaction energy: Endothermic
If it could happen, I am fairly certain the reaction itself would be endothermic, as there’s a whole lot of energy required to form those O-O bonds. The resulting explosion would be exothermic, though.

[1] A.D. Kirk, The Thermal Decomposition of Methyl Hydroperoxide, Can J Chem 43, 1965