Phosphorous pentoxide is the usual name because that the compound with a chemistry formula P4O10. Phosphorus pentoxide is a covalent compound the is created of 4 phosphorus (P) atoms and 10 oxygen (O) atoms. It occasionally referred to as diphosphorus pentoxide, phosphoric anhydride, and also tetra phosphorus decoxide.

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“Without phosphorous, there would certainly be no thoughts.” — Ludwig Buchner


Phosphorous pentoxide is a solid, white, waxy substance at room temperature and comes in 4 unique crystalline structures. It is an anhydride the phosphoric acid and is an extremely hygroscopic, meaning that it readily absorbs water from the surrounding atmosphere. Together such, phosphorous pentoxide is frequently used as a desiccant to keep areas dry and totally free from airborne moisture.

While being stored, phosphorous pentoxide will react with the environment to kind a skin of phosphoric acid about the compound. This class of acid can prevent phosphorous pentoxide from illustration water out of the air, which deserve to make it less reliable as a desiccant. To prevent this, phosphorous pentoxide is commonly processed right into a granular form for desiccant use. Historically, phosphorus pentoxide was developed via a reaction v white phosphorus and also oxygen, however other much more efficient methods of production have actually taken precedence.

Molecular Vs. Empirical Formula

An astute leader may notice something strange. What is the compound through the chemistry formula P4O10 named phosphorous pentoxide? after all, pent- is the prefix of chemistry nomenclature meaning “five”, and also the formula P4O10 clearly suggests that there room 10 oxygens. What gives?

In chemistry, there are 2 type of chemical formulas, the molecule formula and empirical formula. Both represent the atomic constituents of a given compound yet in various ways. The molecular formula speak you the type and number of atoms in a free-standing solitary molecule that the compound. The empirical formula tells you the most basic integer proportion of facets in a compound. 2 compounds might have same various molecular formulas and the very same empirical formula, such together acetylene (C2H2) and benzene (C6H6), both of i beg your pardon share the empirical formula that CH. Likewise, the empirical formula for both ethylene (C2H4) and butene (C4H8) is CH2. A compound’s molecule formula is either equal to or is a totality number lot of of that empirical formula.


Sometimes, the common name because that a compound is acquired from the empirical formula rather of its molecule formula. Such is the instance with phosphorus dioxide. Phosphorus pentoxide has a molecular formula of P4O10 and so has an empirical formula the P2O5. The “pent-” in “pentoxide” originates from the empirical formula P2O5. 

In the instance of phosphorus pentoxide, molecules through a formula of P2O5 will certainly associate through each various other to kind larger molecule of P4O10. So also though the molecular formula that phosphorus pentoxide is P4O10, the is still referred to as phosphorus pentoxide top top account that its empirical formula P2O5.

Phosphorus Pentoxide: physics Properties

“Who to know whether that is not true the phosphorous and mind space not the exact same thing?” — Stendhal

Phosphorous pentoxide is unique in the it deserve to exist in approximately 4 unique polymorphs. The many common type is a solitary molecule the P4O10, which creates from the cohesion that two smaller sized P2O5 molecules. P2O5 has actually a an extremely unstable molecular configuration, so 2 molecules will sign up with up to because that a larger single molecule the P4O10, and arrange themselves according to the complying with diagram:

This certain configuration is structured together 4 tetrahedra, every sharing a leg v another. Each tetrahedron is created of a main phosphorus atom surrounding by 4 oxygen atoms, where the 3 base oxygen atom of each tetrahedron room shared. A single molecule the phosphorus pentoxide watch a small like a small hexagonal cell through terminal oxygen atoms protruding indigenous the sides. The specific configuration that the molecules makes phosphorus pentoxide less dense than many crystalline solids, v a density of just 2.3 g/cm3. The geometric structure of phosphorus pentoxide is comparable to the hydrocarbon crystal adamantane and it has actually a fairly high melting suggest for covalently bonded compounds at 340 °C. The boiling point of phosphorus pentoxide is just 20 °C greater than its melt point, so it will frequently skip melting and sublime straight into a gas.


The hexagonal cell of a molecule that phosphorus pentoxide is organized together by weak van der Waals forces—the electrostatic attraction between molecules. Phosphorus pentoxide contains 6 P–O–P bonds and 4 P=O bonds. The dipole-dipole interactions of the P–O–P bonds space what keep the molecule together. P–O–P bonds room polar through a an adverse valence top top the oxygen atom.

All the polymorphs of phosphorus pentoxide room based approximately tetrahedral species of phosphorus and also oxygen atoms. They typically are created with P=O double bonds such together the o’-(P2O5) type shown below.

Many the the polymorphs have actually a slightly different molecular plan than continuous phosphorus pentoxide. Because that instance, the secure “O” kind consists the cyclical arrangements of P6O6 rings, comparable to the framework of assorted silicate minerals. Among phosphorus pentoxide’s polymorphs is an amorphous glass produced by fusing together any kind of two various polymorphs.

Phosphorus Pentoxide: chemistry Properties

Phosphorus pentoxide is a polar compound. The electronegativity difference between oxygen and phosphorus is 1.4, making P-O bonds quite polar in nature. Also though phosphorus pentoxide is polar, it will certainly not be liquified by water because it instead undergoes exothermic hydrolysis. Phosphorus pentoxide is one anhydride, meaning that it is created by removed water (H2O) indigenous a compound. Phosphorus pentoxide is the matching anhydride of phosphoric acid (H3PO4) and also will reaction violently through water to form phosphoric, follow to the equation:

P4O10 + 6H2O → 4H3PO4

The enthalpy of change of this reaction is -177 kJ/mol, meaning that because that every 1 mole that P4O10, 177 kJ of energy are exit in the kind of heat. This reaction with water is just one of the key methods for developing industrial amounts of phosphoric acid, really important ingredient in fertilizers.

Phosphorus pentoxide is non-combustible and will no react v oxygen to produce a flame. However, the hydrolysis reaction of phosphorus pentoxide with water and water-containing substances like wood is really exothermic and can release enough power to catalyze a burning reaction in between the water-containing material and also the atmosphere. Phosphorus pentoxide is an extremely corrosive to metal and also will form various metal oxides and also phosphate steels when brought into call with metals. It is also really corrosive to person tissue and can cause chemical burns and also respiratory inflammation, also at low concentrations.

Phosphorus Pentoxide: Production and Use

Historically the primary technique of creating phosphorus pentoxide is v the burning of elemental phosphorus and oxygen. White phosphorus, one of the allotropes of elemental phosphorus, is make of molecules composed of 4 phosphorus atoms arranged in a tetrahedral structure. Elemental tetra phosphorus burns in oxygen to kind phosphorus pentoxide follow to the following reaction:

P4 + 5O2 → P4O10

Most phosphorus pentoxide developed in this way is for the function of do phosphoric acid, though recent methods have actually removed the must start through white phosphorus to make phosphoric acid.

The key use that phosphorus pentoxide is together a desiccant. Due to the fact that it reacts readily with water, phosphorus pentoxide can attract traces that water the end of the setting to keep a an are dry and also moisture-free. The hydrolysis that water through phosphorus pentoxide create a gummy layer of phosphoric acid that can inhibit the water-removing properties. This is why many phosphorus pentoxide offered for industrial purposes is made in a granular form. The is not feasible to kind phosphorus pentoxide via the dehydration that phosphoric acid, together the heat required to catalyze the reaction is sufficient to boil off any type of excess water.

The desiccant nature of phosphorus pentoxide are frequently used to transform a number of acids right into their equivalent anhydrides. Because that instance, phosphorus pentoxide will transform nitric acid (HNO3) right into its anhydride dinitrogen pentoxide (N2O5). The will also convert sulfuric mountain (H2SO4) right into sulfur trioxide (SO3) by remove one oxygen and also two hydrogens; a solitary molecule of water, and it will convert hydrogen perchlorate (HClO4) into dichlorine heptoxide (Cl2O7).

“We define organic chemistry together the chemistry of carbon compounds.” — respectable Kekule

The majority of phosphorus pentoxide the is not used as a desiccant is provided as one intermediary reactant to create other compounds. In organic chemistry, phosphorus pentoxide is offered to dehydrate essential compounds, like converting amides right into nitriles, an essential class of necessary molecules used in rubber manufacturing and lab procedures.

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In summary, phosphorus pentoxide is an anhydride covalent compound the is developed via the burning of element phosphorus and also oxygen. Phosphorus pentoxide is very hygroscopic, so that will attract water out of the adjacent environment and also react to kind phosphoric acid. Phosphorus pentoxide is usually used together an industrial desiccant and plays a duty as an intermediate reactant to revolve acid right into their anhydride counterparts. Even though a solitary molecule of the compound has actually a molecular formula the P4O10, it is still referred to as phosphorus pentoxide top top account of its empirical formula P2O5. Phosphorus pentoxide is unique in that it exist in several different polymorphs that have various molecular geometries. The many common form is a hexagonal cell created of 4 distinctive phosphorus tetrahedra. Phosphorus pentoxide is corrosive come metals and also can damage human tissue also in little concentrations.