Oxyhydrogen

Oxyhydrogen gas, known in the English speaking also oxyhydrogen, is a detonating mixture of gaseous hydrogen ( H2) and oxygen ( O2). Upon contact with open fire ( embers or sparks ), the so-called oxyhydrogen reaction. A finished mixture of hydrogen and oxygen in a 2:1 ratio is explosive, even in small quantities. One uses, however, only hydrogen as a raw material and mixes it with air under atmospheric pressure, the volume fraction of the hydrogen 4-77 % must be. If these limits are exceeded or fallen short, there is no longer an explosion / detonation. By controlled combustion in a mixing nozzle, continuous oxyhydrogen flame can be achieved.

Production

Oxyhydrogen can be explained by the electrolysis of water, so the electrolytic decomposition of water ( H2O) or produced by the thermal decomposition of water. The thermal decomposition of water requires temperatures in excess of 2500 ° C.

In water electrolysis, the splitting is carried out with the aid of electric current. The electrodes are immersed in water that has been made ​​electrically conductive by the addition of some acid, preferably sulfuric acid, or alkali. For safety's sake, the high pearling of the two electrodes gases are separated - ie the hydrogen on the cathode ( negative pole) - collected, The use of sodium chloride as the electrolyte is possible, depending on the used electrodes and current density in addition to or instead of oxygen and releasing chlorine.

Oxyhydrogen reaction

The oxyhydrogen reaction is an exothermic and detonation -like ongoing reaction of hydrogen with oxygen and proceeds with a detonation velocity of 2,820 m / s It is a form of combustion ( oxidation).

The reaction equation is:

Is a highly branched chain reaction ( chain branching explosion) involving hydrogen, oxygen and hydroxyl radicals as chain carrier.

And other reactions

The reaction product is water.

The per molar formula sales released energy is 571.6 kJ / mol ( ΔrH0 = -571.6 kJ / mol). So that the enthalpy change H to one mole of the resulting water to -286 kJ / mol.

As a side reaction, hydrogen peroxide is formed according to:

In the mitochondria of living cells occurs in the terminal oxidation in complex IV in the respiratory chain to an analogous, but strictly controlled exergonic reaction (sometimes, not entirely accurate, as " biological oxyhydrogen reaction ") that the h of the cell's energy, d the formation of ATP molecules is used:

The Gibbs free energy DG ° 'of the reaction arises from its redox potential ( 0.5 V) and is at physiological conditions (pH 7) -193 kJ / mol.

The same reaction also takes place in the fuel cell. Free enthalpy or Gibbs energy? G used without causing an explosion: When the construction is in the oxyhydrogen reaction released energy ( enthalpy ), more precisely here. The enthalpy released in the process is released in part as an electric current, and partly as heat. However, the reaction proceeds slowly in the fuel cell and under control.

Oxyhydrogen gas sample

The term explosive gas sample is referred to in the chemical detection of hydrogen. However, this is non-specific, as well as methane with oxygen forms hydrogen-oxygen, and is only used in chemistry classes as pseudo- evidence. Actual use (see below) is the checking of the air content of a hydrogen -producing apparatus.

For the detection usually the gas to be tested is in a test tube with the opening downwards (so that hydrogen due to the lower density than air can not escape ) held on an ignition source ( Bunsen burner, lighter).

Case 2: The collected gas is a mixture of hydrogen and oxygen ( oxyhydrogen ). The combustion takes place with a whistling noise (positive oxyhydrogen sample).

Due to the different noise in pure hydrogen, and the mixture of hydrogen with oxygen, the oxyhydrogen sample is also used to verify the purity of hydrogen gas in order to prevent an explosion in a closed vessel.

Similar oxyhydrogen explodes the chlorine and hydrogen gas.

Application

The fact that the hydrogen-oxygen reaction may also be set by a platinum wire as a catalyst in transition, discovered Johann Wolfgang Dobereiner. Some years later, the inflammation of a detonating gas mixture he succeeded under the influence of platinum sponge. This discovery led to the invention of the first lighter ( the Döbereinerschen platinum lighter ).

Accidents

Worldwide there have been many accidents caused by oxyhydrogen explosions, some of them catastrophic. For example, the crash of the Hindenburg zeppelin in 1937, where the approach to the mooring mast by a smaller leak the carrier gas hydrogen escaped into the air atmosphere and thus a huge hydrogen fire was caused.

More recently, particularly known were hydrogen explosions in 1986 at the Chernobyl disaster and 2011 at the Fukushima nuclear disaster.