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In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by naming the gas from a metal-acid reaction "inflammable air". He speculated that "inflammable air" was in fact identical to the hypothetical substance " phlogiston " [ 80 ] [ 81 ] and further finding in 1781 that the gas produces water when burned.
The lifting power in air of hydrogen and helium can be calculated using the theory of buoyancy as follows: Thus helium is almost twice as dense as hydrogen. However, buoyancy depends upon the difference of the densities (ρ gas) − (ρ air) rather than upon their ratios. Thus the difference in buoyancies is about 8%, as seen from the buoyancy ...
Liquid hydrogen (H 2 (l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H 2 form. [4] To exist as a liquid, H 2 must be cooled below its critical point of 33 K. However, for it to be in a fully liquid state at atmospheric pressure, H 2 needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F). [5]
Hydrogen has a wide flammability range (3–70% H 2 in air) in comparison with other fuels. [35] As a result, it can be combusted in an internal combustion engine over a wide range of fuel-air mixtures. An advantage of this is the engine can be run using a lean fuel-air mixture.
High pressure electrolysis is the electrolysis of water by decomposition of water (H 2 O) into oxygen (O 2) and hydrogen gas (H 2) by means of an electric current being passed through the water. The difference with a standard electrolyzer is the compressed hydrogen output around 120–200 bar (1740–2900 psi , 12–20 MPa ). [ 146 ]
For a fuel of composition C c H h O o N n, the (higher) heat of combustion is 419 kJ/mol × (c + 0.3 h − 0.5 o) usually to a good approximation (±3%), [2] [3] though it gives poor results for some compounds such as (gaseous) formaldehyde and carbon monoxide, and can be significantly off if o + n > c, such as for glycerine dinitrate, C 3 H 6 ...
The formula for acyclic saturated hydrocarbons (i.e., alkanes) is C n H 2n+2. [1]: 623 The most general form of saturated hydrocarbons, (whether linear or branched species, and whether with or without one or more rings) is C n H 2n+2(1-r), where r is the number of rings. Those with exactly one ring are the cycloalkanes.
At standard temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume. [5] [4] When ignited, the gas mixture converts to water vapor and releases energy, which sustains the reaction: 241.8 kJ of energy for every mole of H 2 burned.