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Burning Hydrogen

10/20/2021 10:48 AM

Burning Hydrogen,

Ok, we all know that Hydrogen can be a great source of energy, if we ever find a way to safely store a decent amount of it easily. And it is more or less pollution free, it's byproduct of it's burning is simply water vapor! BUT.... And there always is a but isn't there?

OK Hydrogen (H2) molecule is made from 2 hydrogen atoms.

Oxygen (O2) is made from 2 Oxygen atoms.

When the Hydrogen burns the H2 Molecule joins with the O2 Molecule, Making water H2O. I guess a plain Oxygen atom is left over? And I would assume it ends up joining with another free Oxygen atom to make O2 oxygen molecule.

So in reality when hydrogen burns it makes as a by-product water vapor and oxygen.

So my question is, OK a 2 atom H2 molecule "Burns" and in doing so, combines with one of the O2 atoms, and makes water vapor. with one oxygen atom left over to simply join with another leftover to make an O2 molecules.

The question is, where is all this energy coming from? Like when you burn H2 in a engine, what is exploding to push the pistons?

Taking H2 and O2 to make water if anything is causing a vacuum because water is much much more dense that the two gasses.

So where is the energy coming from, since nothing of the two gasses is not accounted for. water and oxygen.

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#1

Re: Burning Hydrogen

10/20/2021 11:18 AM

You are overlooking something. Actually two H2 molecules combine with one O2 molecule. The result is two H2O molecules and a lot of heat

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#2
In reply to #1

Re: Burning Hydrogen

10/20/2021 11:45 AM

Where is this "HEAT" coming from?

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#3
In reply to #2

Re: Burning Hydrogen

10/20/2021 11:52 AM

Exothermic chemical reaction...

"A particularly important class of exothermic reactions is combustion of a hydrocarbon fuel, e.g. the burning of natural gas:

{\displaystyle {\ce {CH4 + 2O2 -> CO2 + 2H2O}}} ΔH⚬ = - 890 kJ/mol

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#13
In reply to #3

Re: Burning Hydrogen

10/22/2021 7:37 AM

"The combustion of ammonia is represented by this equation: 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) ΔH°rxn = -904.8 kJ "

https://www.clutchprep.com/chemistry/practice-problems/11187/the-combustion-of-ammonia-is-represented-by-this-equation-4nh3-g-160-5o2-g-160-8

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#16
In reply to #13

Re: Burning Hydrogen

10/28/2021 9:27 PM
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#4

Re: Burning Hydrogen

10/20/2021 10:00 PM

Hydrogen can be burned in an internal combustion engine, but efficiency is low, about 20% (Carnot efficiency). This is because the chemical energy is converted to heat, which is then converted into mechanical energy.

Fuel cells convert the energy of the hydrogen-oxygen reaction directly into electricity at a much higher efficiency (up to 60%), and electric motors which convert electricity into mechanical energy are highly efficient.

"The gasoline engine in today’s typical car is less than 20% efficient in converting the chemical energy in gasoline into power that moves the vehicle, under normal driving conditions. Fuel cell vehicles, which use electric motors, are much more energy efficient. The fuel cell system can use 60% of the fuel’s energy—corresponding to more than a 50% reduction in fuel consumption compared to a conventional vehicle with a gasoline internal combustion engine. When using hydrogen produced from natural gas, fuel cell vehicles are expected to have well-to-wheels greenhouse gas emissions less than half that of current gasoline-powered vehicles."

https://www.energy.gov/sites/prod/files/2015/11/f27/fcto_fuel_cells_fact_sheet.pdf

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#5

Re: Burning Hydrogen

10/21/2021 1:06 AM

Bond energy. All atom-to-atom bonds have an energy value that is needed to break them. In a reaction, the new bonds have such values too. Energy is measurable, convertible among many forms, and never disappears.

Hydrogen by itself is not available on earth. We can get it from water, where it was already combined, It takes energy to break those H-O bonds but we get much of that back when we burn it (oxidize). These numbers are known, but conveniently ignored by those anxious to see hydrogen as an environmental savior. Its combustion doesn't make carbon dioxide and thus is supposed to slow down global warming, but HMM (How Much Matters). And the energy to break the bonds to get the hydrogen from water may come from combustion of carbon-containing molecules. Hydrogen may in fact come out OK after all is said and done, but make sure you hear it all before you're done.

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#6
In reply to #5

Re: Burning Hydrogen

10/21/2021 5:19 AM

<...may come from combustion of carbon-containing molecules...>

Ideally it comes from sunlight. That's the whole point. There is no point in making hydrogen by burning fossil fuels!

Hydrogen is an energy carrier, much like electricity.

https://en.wikipedia.org/wiki/Hydrogen_fuel

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#7
In reply to #6

Re: Burning Hydrogen

10/21/2021 7:47 AM

As of 2020, about 95% of hydrogen is produced by the gasification of fossil fuels, which produces CO2 in someone else's backyard.

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#9
In reply to #7

Re: Burning Hydrogen

10/21/2021 8:00 AM

Old news.

Where is the trend-line going?

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#12
In reply to #9

Re: Burning Hydrogen

10/21/2021 10:39 PM

Seems to be heading for ammonia(NH3), much easier to store and ship, more energy dense than liquid hydrogen, simple to make with hydrogen and nitrogen...but still expensive comparatively speaking to fossil fuels....

..." Ammonia has a higher energy density, at 12.7 MJ/L, than even liquid hydrogen, at 8.5 MJ/L. Liquid hydrogen has to be stored at cryogenic conditions of –253 °C, whereas ammonia can be stored at a much less energy-intensive –33 °C. And ammonia, though hazardous to handle, is much less flammable than hydrogen....

...By most estimates, green ammonia will cost two to four times as much to make as conventional ammonia. And some of the technologies needed to harness the molecule, such as ammonia-burning engines, are still experimental....

...Furthermore, thanks to a century of ammonia use in agriculture, a vast ammonia infrastructure already exists. Worldwide, some 180 million metric tons (t) of ammonia is produced annually, and 120 ports are equipped with ammonia terminals....

...Several much larger projects were announced last year. By far the most ambitious one is in Saudi Arabia. The $5 billion project is a partnership between the US company Air Products and Chemicals, the local firm ACWA Power, and NEOM, a developer building a carbon-free city in Saudi Arabia.

Slated for completion in 2025, the installation will sit on the Red Sea coast. Solar cells will harness the sun during the day, while turbines will capture nighttime winds to generate 4 GW of electricity for water electrolysis plants. The hydrogen will be fed into a traditional Haber-Bosch plant to produce 1.2 million t per year of ammonia—a large amount even by conventional standards.

Air Products will spend an additional $2 billion to set up a novel distribution scheme. It will ship the ammonia around the world to specialized plants installed at depots for buses and trucks fueled by hydrogen cells. These units will dissociate the ammonia to recover the hydrogen, enough for up to 15,000 trucks and buses in all."....

https://cen.acs.org/business/petrochemicals/ammonia-fuel-future/99/i8

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#10
In reply to #7

Re: Burning Hydrogen

10/21/2021 9:43 AM

One of the Holy Grails that catalysis scientists hope to eventually make Hydrogen fuel widely practical is not a catalysis procedure that splits water molecules into hydrogen and oxygen for energy storage. As the Wikipedia link subsection discusses, simple electrolysis of water is fairly efficient. Thus catalysis has little room to improve efficiencies. The primary complication for Hydrogen fuel is hydrogen storage and the energy needed to put Hydrogen into and out of storage.

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#8

Re: Burning Hydrogen

10/21/2021 7:57 AM

The experts here might be able to say the combined mass of two H2O water molecules is less than the combined mass of two H2 molecules and one O2 molecule.

E=MC2...that might explain where the energy comes from....assuming C does not change during the process ... and Einstein is right...!

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#11
In reply to #8

Re: Burning Hydrogen

10/21/2021 12:56 PM

Energy has to go IN to separate the H from the O, and the H-H and O-O bond energies are different from H2O, hence the mass difference. When it recombines in combustion the bonds are remade, but we still need the energy IN to separate. And we need to get THAT from nonfossil before we can claim an enviro benefit (another critical issue involving CO2 in oceans, too big to bring in here).

There are practical problems like storage which may be resolved, but no miracles in science. That's why so many people are uncomfortable with science, as we learn miracles in babyhood when nothing can be explained, and it gets reinforced in a make-believe childhood (look at Halloween) and relied on as adults to keep us functionally sane.

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#14

Re: Burning Hydrogen

10/22/2021 8:37 AM

Maybe a gasoline/ammonia fuel mixture would work....?

"Can you mix gasoline and ammonia?

The use of ammonia with gasoline allowed knock-free operation with MBT spark timing at higher compression ratios and higher loads than could be obtained with the use of gasoline alone."

"An overall stoichiometric mixture of air, gaseous ammonia, and gasoline was metered into a single cylinder, variable compression ratio, supercharged cooperative fuel research (CFR) engine at varying ratios of gasoline to ammonia.

The engine was operated such that the combustion was knock-free with minimal roughness for all loads ranging from idle up to a maximum load in the supercharge regime.

For a given load, speed, and compression ratio, there was a range of ratios of gasoline to ammonia for which knock-free, smooth firing was obtained. This range was investigated at its rough limit and also at its maximum brake torque (MBT) knock limit.

If too much ammonia was used, then the engine fired with an excessive roughness. If too much gasoline was used, then knock-free combustion could not be obtained while the maximum brake torque spark timing was maintained.

Stoichiometric operation on gasoline alone is also presented, for comparison. It was found that a significant fraction of the gasoline used in spark ignition engines could be replaced with ammonia. Operation on about 100% gasoline was required at idle. However, a fuel mix comprising 70% ammonia/30% gasoline on an energy basis could be used at normally aspirated, wide open throttle.

Even greater ammonia to gasoline ratios were permitted for supercharged operation. The use of ammonia with gasoline allowed knock-free operation with MBT spark timing at higher compression ratios and higher loads than could be obtained with the use of gasoline alone."

https://www.researchgate.net/publication/228372050_The_Fuel_Mix_Limits_and_Efficiency_of_a_Stoichiometric_Ammonia_and_Gasoline_Dual_Fueled_Spark_Ignition_Engine

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#15
In reply to #14

Re: Burning Hydrogen

10/22/2021 9:45 AM

I wonder what they could get away with if it was a fuel injected type of fuel delivery system?

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