أكاديميا - كولنز - معاجم الجيب العلمية - الكيمياء - انكليزي - فرنسي - عربي الحرف ١_ h

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Haber process
Procédé m de Haber

Haber process. Ammonia is made in this process from hydrogen and nitrogen. Nitrogen is taken from air and hydrogen from improving natural gas reforming. The two gases react together in a ratio of 3:1 at a temperature of 500°C and a pressure of 200 atmospheres. An iron mediator is used: iron catalyst.

N2 (gas) + 3H2 (gas) → 2NH3 (gas)

This process is an equilibrium reaction whose conditions are chosen to produce the largest possible amount of ammonia in the shortest possible time. Under these conditions, about 15 percent of the two reacting substances are transformed into ammonia. A lower temperature can generate “more” ammonia, but at a much slower rate. Conversely, using a higher temperature generates ammonia more quickly but with a lower yield. The conditions chosen are the optimal conditions.


haemoglobin
hemoglobin m

Hemoglobin. roe. The red pigment found in red blood cells. It contains an iron atom in a complex molecule. Oxygen reacts with the dye to form oxyhaemoglobin, releasing oxygen from the compound where it is needed. Carbon monoxide also reacts with hemoglobin to form carboxyhaemoglobin, which is a very stable compound that prevents oxygen transport. This is why carbon monoxide is an extremely dangerous poison. It is necessary for the body to obtain enough iron daily to maintain the correct levels of hemoglobin, and the daily need for it is about 11 mg. Iron deficiency leads to paleness or anemia.

half-life
period f

Half-life When a radioactive isotope gives up beta particles or alpha decays it turns into a different isotope. As decay occurs, the number of nuclei becomes smaller. The half-life of an isotope is the time it takes for radioactivity to drop to half its original value. The decay of an isotope can usually be tracked by measuring the rate of particle emission. This rate is directly proportional to the number of cores present.

The graph shows the decay of an isotope with a half-life of one minute, meaning that the number of particles emitted is halfway through each minute,
For example, 1000 - 2000 - 4000. . Etc. There is a large difference in the length of the half-life from one isotope to another. But the half-life of each isotope is constant under all conditions of temperature and pressure.

Number of particles released per minute:
4000
3000
2000
1000
500
0

Time/minutes
0
1
2
3
4
5

Isotope - half-life

Carbon - 5730 - 14 years
Oxygen - 14 - 20 seconds
Copper - 756 - 64 minutes
Uranium - 250,000 - 234 years


half-action
demi-reaction f

Half-reaction It is often useful to represent a reaction in terms of two half-reactions, such as the displacement of zinc to copper ions from a solution:

Cu2+ + Zn → Zn2+ + Cu
(solid) (aqueous) (solid) (aqueous)

The equation can be represented as:

(a) (solid) → -2e + (aqueous) +Cu2

(b) -2e + (aqueous) Zn2 → (solid) Zn

It is easy to see from these two half-reactions that the zinc is oxidized by the copper ions, and the copper ions are returned. Half-reactions are useful in looking at reduction and oxidation reactions.

halide
halide m

Halide. A halogen compound with another element.
Examples:

Hydrogen chloride (HCI) Sodium bromide (NaBr) Calcium fluoride (CaF2) Silicon tetrachloride (SiCl4)
Metal halides tend to be ionic, while non-metal halides have covalent bonds. Metal halides can be produced from the interaction of elements with each other:

2Na (solid) + Cl2 (gas) → 2NaCl (solid)


halogens
halogènes mpl

Halogens. Elements in the group of the periodic table. All of them are toxic non-metallic elements. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid at normal temperature. All of these elements are oxidizing agents, and their oxidizing capacity and chemical reactivity decrease in the following order:

F2 > Cl2 - Bra > 12,
That is, the group is descending

Halogens react strongly with metals and hydrogen, forming halides.
They all contain seven electrons in the outer shell of the atom and form monovalent stalagmites, such as -CI-Br.