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Academia - Collins - Pocket Scientific Dictionaries - Chemistry - English - French - Arabic Letter 4_ P


photosynthesis
photosynth f

Photosynthesis. A photochemical process in which carbon dioxide and water are converted into carbohydrates and oxygen.


6CO2 + 6H2O → C6H12O2 + 802
(gas) (solid) (liquid) (gas)

This process occurs in the leaves of plants and is the means by which plants obtain their food, in addition to returning oxygen to the atmosphere.

Chlorine and chlorophyll act as mediators in this reaction, while sunlight provides the necessary energy for it.


physical change
transformation of physics

Physical change. Physical change of matter includes change
Its physical properties without any modifications to its chemical properties.


physical chemistry
chimie f physique

physical chemistry. Studying the physical properties of elements and compounds and the relationship between their chemical and physical properties.


pipette
pipette f

Suck. A glass instrument used to measure a specific volume of liquid, such as 25 cm3, and move it to another location.

The liquid is drawn into the pipette through an opening at the bottom by sucking at the open point S. The liquid continues to be withdrawn until the bottom of the crescent surface of the liquid is gradually reached.

To empty the liquid from the pipette, the sucking is stopped and the lower hole is placed in contact with the wall of the vessel, so the liquid flows into it. In this case, the pipette empties exactly the correct volume of liquid.
See burette.

planar
plan m

flat. A planar molecule is a molecule in which all of its atoms are in the same plane, that is, it is flat. All linear and tri-atomic molecules must be planar. Boron trifluoride is a planar molecule.
HCI
N2

CO
NO2

C2H2
SiO2

H2O
CO2

Most carbon compounds are “nonplanar” due to the tetrahedral arrangement of atoms around the carbon atom. Most alkenes are non-planar, with the exception of prone, which is non-planar because three hydrogen atoms are attached to a carbon atom and are located above or below the other atoms.


plastic
plastic m

Plastic. Plastic can be shaped or molded by heat and pressure. This name is usually used to describe man-made polymers, such as poly(ethene), nylon, etc. There are more than thirty different types of ionomers, and today it is possible to combine them to produce man-made materials with specific properties.
See thermoplastic and thermosetting.


platinum
platinum m

Platinum is a transition metal used as a catalyst in the chemical industry. It is also used as a jewelry metal and as an inert pathway in electrolysis. It is an expensive metal due to its benefits and scarcity, and it is found in nature as an element.


plutonium
plutonium m

plutonium. Man-made item. And he makes this
The element in atomic reactors is the isotope 238 of uranium by absorbing a neutron:



unstable
239/92U + 1/0n →
238/92U

(beta particle)
239/92U → 239/93Np + - 0/1e

Neptunium-239 is also unstable:

(beta particle)
239/93Np → 239/94U + - 0/1e

Uranium-239 and neptunium-239 have a half-life of 20 minutes for the first and two days for the second, and they decay quickly. The half-life of plutonium is more than 24,000 years, and therefore it is very stable.

Plutonium is used in bombs and as fuel for nuclear reactors, such as the fast breeder reactor. The cores of these reactors are surrounded by uranium-238, which is connected in the manner described above to plutonium-239 while the reactor is operating. In this way fuel can be produced
More than that used in the reactor.

Plutonium is a toxic and dangerous chemical and must be handled with extreme care. There is great controversy surrounding its use.