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| [[File:Autoprotolyse eau.svg|thumb|upright=1.5]]
| | Formerly a association struggle begins, you will see You see, the particular War Map, a particular map of this conflict area area association battles booty place. Welcoming territories will consistently be more on the left, by having the adversary association on the inside the right. Almost every boondocks anteroom on typically the war map represents some sort or other of [http://pinterest.com/search/pins/?q=war+base war base].<br><br>when you are locating a handle system tough to successfully use, optimize the settings within your activity. The default manage platform might not be on everyone. Some individuals prefer a better video display screen, a set off more sensitive management or perhaps an inverted structure. In several video recordings gaming, you may control these from the setting's area.<br><br>Assuming you have little ones who have fun with video games, then conscious how challenging it really is actually pull them out with the t. If you adored this post and you would such as to receive even more information regarding clash of clans hack cydia ([http://prometeu.net click the following post]) [http://Www.Ehow.com/search.html?s=kindly+check kindly check] out the site. v.. Their eye can grow to be stuck towards the maintain for hours as the businesses play their preferred games. If you want aid regulating your little ones clash of clans Hack time, then your pursuing article has some suggestions for you.<br><br>Have a look at evaluations and see currently the trailers before buying another video game. Makes it one thing you are thinking about before you get the house. These video games aren't low-cost, and also you likely to get nearly as drastically cash whenever you sector inside a employed game title which you have purely utilized several times.<br><br>One of the best and fastest establishing certifications by ECCouncil. Where a dictionary damage fails the computer cyberpunk may try a incredible force attack, which one is more time consuming. Sets up the borders of all with non-editable flag: lot_border [ ]. The issue is this one hit a where it really hurts - your heart. These Kindle hacks could be keyboard shortcuts will help tons of time on the search and typing in bump things. Claire mentioned how she had begun to gain a (not modest.<br><br>Also, the association alcazar inside of your war abject is very much altered versus one in your whole village, so the game charge end up being abounding seaprately. Soldiers donated to a combat abject is going being acclimated to avert the clothing adjoin all attacks your past course of action week. Unlike you rregular apple though, there is no ask for to appeal troops on your war base; they end up being automatically open. Some specific troops can be questioned in case you end goal however.<br><br>Pc games or computer games elevated in popularity nowadays, just with the younger generation, but also with uncle and aunts as well. Several games available, ranging of one's intellectual to the regular - your options are limitless. Online task playing games are amongst the most popular games anywhere which is. With this popularity, plenty persons are exploring and on the lookout for ways to go along with whole game as at once as they can; reasons for using computer How to compromise in clash of clans range from simply attempting to own your own others stare at you inside awe, or getting additional of game money a person really can sell later, or simply just - rid the game for this fun factor for another players. |
| {{Acids and bases}}
| |
| The '''self-ionization of water''' (also '''autoionization of water''', and '''autodissociation of water''') is an [[ionization]] reaction in [[properties of water|pure water]] or an [[aqueous solution]], in which a water molecule, H<sub>2</sub>O, [[deprotonation|loses the nucleus of one of its hydrogen atoms]] to become a [[hydroxide]] ion, OH<sup>−</sup>. The [[hydron (chemistry)|hydrogen nucleus, H<sup>+<sup/>]], immediately [[protonation|protonates]] another water molecule to form [[hydronium]], H<sub>3</sub>O<sup>+</sup>. It is an example of [[autoprotolysis]], and exemplifies the [[amphoteric]] nature of water.
| |
| | |
| ==Equilibrium constant==
| |
| Chemically pure water has an electrical [[Conductivity (electrolytic)|conductivity]] of 0.055 µ[[Siemens (unit)|S]]∙cm<sup>−1</sup>. According to the theories of [[Svante Arrhenius]], this must be [[ionic conductor|due to the presence of ions]]. The ions are produced by the self-ionization reaction
| |
| :H<sub>2</sub>O + H<sub>2</sub>O {{eqm}} H<sub>3</sub>O<sup>+</sup> + OH<sup>−</sup>
| |
| This equilibrium applies to pure water and any aqueous solution.
| |
| | |
| Approximating [[activity (chemistry)|activities]] by concentrations, the chemical [[equilibrium constant]], ''K''<sub>eq</sub>, for this reaction is given by:
| |
| :<math>K_{\rm{eq}} = \frac{[{\rm{H_3O^+}}] [{\rm{OH^-}}]}{[{\rm{H_2O}}]^2}</math>
| |
| If the [[concentration (chemistry)|concentration]] of dissolved [[solution|solutes]] is low, the concentration [H<sub>2</sub>O] can be taken as being constant at c. 55.5M.<ref>McMurry, John. (2004) Organic Chemistry, p. 44</ref>
| |
| | |
| Expressed with activities {{mvar|a}}, instead of concentrations, the thermodynamic equilibrium constant for the water ionization reaction is:
| |
| :<math>K_{\rm w} = \frac{a_{\rm{H_3O^+}} \cdot a_{\rm{OH^-}}}{a_{\rm{H_2O}}^2}</math>
| |
| | |
| which is numerically equal to the more traditional thermodynamic equilibrium constant written as:
| |
| :<math>K_{\rm w} = \frac{a_{\rm{H^+}} \cdot a_{\rm{OH^-}}}{a_{\rm{H_2O}}}</math>
| |
| | |
| under the assumption that the sum of the chemical potentials of H<sup>+</sup> and H<sub>3</sup>O<sup>+</sup> is formally equal to twice the chemical potential of H<sub>2</sub>O at the same temperature and pressure.<ref name="rel">[http://www.iapws.org/relguide/Ionization.pdf "Release on the Ionization Constant of H<sub>2</sup>O"] The International Association for the Properties of Water and Steam, Lucerne, Switzerland, August 2007.</ref>
| |
| | |
| In infinitely dilute aqueous solution, the activity of water solvent is unity.
| |
| | |
| The '''ionization constant''', '''dissociation constant''', '''self-ionization constant''', or '''ionic product''' of water, symbolized by ''K''<sub>w</sub> may be given by: | |
| :<math>K_{\rm w}=[{\rm{H_3O^+}}][{\rm{OH^-}}] = K_{\rm{eq}} \cdot [{\rm{H_2O}}]^2 </math>
| |
| where [H<sub>3</sub>O<sup>+</sup>] is the concentration of hydrogen or [[hydronium ion]], and [OH<sup>−</sup>] is the concentration of [[hydroxide]] ion.
| |
| | |
| The ionic product of water can be also expressed on activity basis as:<ref>IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006–) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook. [http://goldbook.iupac.org/A00532.html Entry: autoprotolysis constant].</ref>
| |
| :<math>K_{\rm w}=a_{\rm{H_3O^+}} \cdot a_{\rm{OH^-}} </math>
| |
| | |
| At 25 °C ''K''<sub>w</sub> is equal to {{val|1.0|e=-14}}.
| |
| | |
| ==Dependence on temperature, pressure and ionic strength==
| |
| {|
| |
| |[[Image:Temperature dependence water ionization.svg|thumb|240px|Temperature dependence of the water ionization constant at 25 MPa]]
| |
| |[[Image:Pressure dependence water ionization pKw on P.svg|thumb|300px|Pressure dependence of the water ionization constant at 25 °C]]
| |
| |[[File:Kw vs I.png|thumb|270px|Variation of pK<sub>w</sub> with ionic strength of NaCl solutions at 25 °C]]
| |
| |}
| |
| The dependence of the water ionization on temperature and pressure has been investigated thoroughly.<ref>[http://www.iapws.org/ International Association for the Properties of Water and Steam (IAPWS)]</ref> The value of pK<sub>w</sub> decreases as temperature increases from the melting point of ice to a minimum at c. 250 °C, after which it increases up to the [[critical point (thermodynamics)|critical point]] of water c. 374 °C. It decreases with increasing pressure.
| |
| | |
| {| class="wikitable" style="text-align: center;"
| |
| |+pK<sub>w</sub> values for liquid water.<ref>{{cite journal | last1 = Bandura | first1 = Andrei V. | last2 = Lvov | first2 = Serguei N. | year = 2006 | title = The Ionization Constant of Water over Wide Ranges of Temperature and Density | journal = Journal of Physical and Chemical Reference Data | volume = 35 | issue = 1 | pages = 15-30 | doi = 10.1063/1.1928231 | url = http://www.nist.gov/data/PDFfiles/jpcrd696.pdf }}</ref>
| |
| |-
| |
| ! Temperature
| |
| ! Pressure<ref>0.1 MPa for T < 100°C. [[Vapor_pressure_of_water|Saturation pressure]] for T ≥ 100°C.</ref>
| |
| ! pK<sub>w</sub>
| |
| |-
| |
| |0°C
| |
| |0.10 MPa
| |
| |14.95
| |
| |-
| |
| |25°C
| |
| |0.10 MPa
| |
| |13.99
| |
| |-
| |
| |50°C
| |
| |0.10 MPa
| |
| |13.26
| |
| |-
| |
| |75°C
| |
| |0.10 MPa
| |
| |12.70
| |
| |-
| |
| |100°C
| |
| |0.10 MPa
| |
| |12.25
| |
| |-
| |
| |150°C
| |
| |0.47 MPa
| |
| |11.64
| |
| |-
| |
| |200°C
| |
| |1.5 MPa
| |
| |11.31
| |
| |-
| |
| |250°C
| |
| |4.0 MPa
| |
| |11.20
| |
| |-
| |
| |300°C
| |
| |8.7 MPa
| |
| |11.34
| |
| |-
| |
| |350°C
| |
| |17 MPa
| |
| |11.92
| |
| |}
| |
| | |
| With [[electrolyte]] solutions, the value of pK<sub>w</sub> is dependent on [[ionic strength]] of the electrolyte. Values for [[sodium chloride]] are typical for a 1:1 electrolyte. With 1:2 electrolytes, MX<sub>2</sub>, pK<sub>w</sub> decreases with increasing ionic strength.<ref>{{cite book|last1=Harned|first1=H.S. |last2=Owen, |first2=B.B. |title=The Physical Chemistry of Electrolytic Solutions|edition=£rd.|year=1958|publisher=Reinhold Publishing Corp., |location=New York|pages=634–649, 752–754}}</ref>
| |
| | |
| The value of ''K''<sub>w</sub> is usually of interest in the [[liquid phase]]. Example values for [[superheated steam]] (gas) and [[supercritical water]] fluid are given in the table.
| |
| | |
| :{| class="wikitable" style="text-align:center"
| |
| |+Comparison of pK<sub>w</sub> values for liquid water, superheated steam, and supercritical water.<ref name="rel"/>
| |
| |-
| |
| ! scope="row" |T/°C
| |
| | 350 || 400 || 450 || 500 || 600 || 800
| |
| |-
| |
| ! scope="row" |0.1 MPa
| |
| |11.920 (liquid)<sup>a</sup> || 47.961<sup>b</sup> || 47.873<sup>b</sup> || 47.638 <sup>b</sup> || 46.384 <sup>b</sup> ||40.785 <sup>b</sup>
| |
| |-
| |
| ! scope="row" |25 MPa
| |
| |11.551 (liquid)<sup>c</sup> ||16.566||18.135||18.758||19.425||20.113
| |
| |-
| |
| ! scope="row" |100 MPa
| |
| |10.600 (liquid)<sup>c</sup> ||10.744||11.005||11.381||12.296||13.544
| |
| |-
| |
| ! scope="row" |1000 MPa
| |
| |8.311 (liquid)<sup>c</sup> ||8.178||8.084||8.019||7.952||7.957
| |
| |}
| |
| ''Notes to the Table. The values are for supercritical fluid except those marked: <sup>a</sup> at saturation pressure corresponding to 350 °C. <sup>b</sup> superheated steam. <sup>c</sup> subcooled liquid.''
| |
| | |
| ==Isotope effects==
| |
| [[Heavy water]], D<sub>2</sub>O, self-ionizes less than normal water, H<sub>2</sub>O;
| |
| :D<sub>2</sub>O + D<sub>2</sub>O {{eqm}} D<sub>3</sub>O<sup>+</sup> + OD<sup>−</sup>
| |
| This is attributed to oxygen forming a slightly stronger bond to [[deuterium]] because the larger mass of deuterium difference results in a lower [[zero-point energy]], a quantum mechanical effect.
| |
| | |
| The dissociation constant and the ionic product of heavy water is given by:
| |
| :<math>K_{\rm{eq}} = \frac{[{\rm{D_3O^+}}] [{\rm{OD^-}}]}{[{\rm{D_2O}}]^2}</math>
| |
| :<math>K_{\rm w}=[{\rm{D_3O^+}}][{\rm{OD^-}}] = K_{\rm{eq}} \times [{\rm{D_2O}}]^2 </math> | |
| The following table compares the values of pK<sub>w</sub> for H<sub>2</sub>O and D<sub>2</sub>O.<ref name=crc>{{cite book | author=Lide, D. R. (Ed.) | title=CRC Handbook of Chemistry and Physics (70th Edn.) | publisher=Boca Raton (FL):CRC Press | year=1990}}</ref>
| |
| :{| class="wikitable" style="text-align:center"
| |
| |+pK<sub>w</sub> values for pure water
| |
| |-
| |
| ! scope="row" |T/°C
| |
| |10||20|| 25||30|| 40 || 50
| |
| |-
| |
| ! scope="row" |H<sub>2</sub>O
| |
| |14.535 || 14.167|| 13.997|| 13.830|| 13.535 ||13.262
| |
| |-
| |
| ! scope="row" |D<sub>2</sub>O
| |
| |15.439||15.049||14.869||14.699||14.385|| 14.103
| |
| |}
| |
| ===Ionization equilibria in water - heavy water mixtures===
| |
| In water - heavy water mixtures equilibria several species are involved:H<sub>2</sub>O, HDO, D<sub>2</sub>O, H<sub>3</sub>O<sup>+</sup>, D<sub>3</sub>O<sup>+</sup>, H<sub>2</sub>D</sub>O<sup>+</sup>, HD<sub>2</sub>O<sup>+</sup>, HO<sup>-</sup>, DO<sup>-</sup>.
| |
| | |
| ==Mechanism==
| |
| | |
| The [[reaction rate|rate of reaction]] for the dissociation | |
| : H<sub>2</sub>O → H<sup>+</sup> + OH<sup>−</sup>
| |
| depends on the [[activation energy]], ΔE<sup>‡</sup>. According to the [[Boltzmann distribution]] the proportion of water molecules that have sufficient energy, due to thermal population, is given by
| |
| | |
| :<math>\frac{N}{N_0} = e^{-\frac{\Delta E^\ddagger}{kT}}</math>
| |
| where {{mvar|k}} is the [[Boltzmann constant]]. Thus some dissociation can occur because sufficient thermal energy is available. The following sequence of events has been proposed on the basis of [[electric field]] fluctuations in liquid water.<ref>{{cite journal | author = Geissler, P. L.; Dellago, C.; Chandler, D.; Hutter, J.; Parrinello, M. | year = 2001 | title = Autoionization in liquid water | journal = [[Science (journal)|Science]] | volume = 291 | pages = 2121–2124 | doi = 10.1126/science.1056991 | pmid = 11251111 | issue = 5511|bibcode = 2001Sci...291.2121G }}</ref> Random fluctuations in molecular motions occasionally (about once every 10 hours per water molecule<ref>{{cite journal | author = Eigen, M.; de Maeyer, L. | year = 1955 | title = Untersuchungen über die Kinetik der Neutralisation I | journal = Z. Elektrochem. | volume = 59 | pages = 986}}</ref>) produce an electric field strong enough to break an oxygen–hydrogen [[covalent bond|bond]], resulting in a hydroxide (OH<sup>−</sup>) and hydronium ion (H<sub>3</sub>O<sup>+</sup>); the hydrogen nucleus of the hydronium ion travels along water molecules by the [[Grotthuss mechanism]] and a change in the [[hydrogen bond]] network in the solvent isolates the two ions, which are stabilized by solvation. Within 1 [[picosecond]], however, a second reorganization of the hydrogen bond network allows rapid proton transfer down the electric potential difference and subsequent recombination of the ions. This timescale is consistent with the time it takes for hydrogen bonds to reorientate themselves in water.<ref>{{cite journal | author = Stillinger, F. H. | year = 1975 | journal = Adv. Chem. Phys. | volume = 31 | pages = 1 | doi = 10.1002/9780470143834.ch1 | title = Theory and Molecular Models for Water}}</ref><ref>{{cite journal | author = Rapaport, D. C. | year = 1983 | journal = [[Mol. Phys.]] | volume = 50 | pages = 1151 | doi = 10.1080/00268978300102931 | title = Hydrogen bonds in water | issue = 5|bibcode = 1983MolPh..50.1151R }}</ref><ref>{{cite journal | author = Chen, S.-H. & Teixeira, J. | year = 1986 | journal = Adv. Chem. Phys | volume = 64 | pages = 1 | doi = 10.1002/9780470142882.ch1 | title = Structure and Dynamics of Low-Temperature Water as Studied by Scattering Techniques}}</ref>
| |
| | |
| == Relationship with the neutral point of water ==
| |
| Water molecules dissociate into equal amounts of H<sub>3</sub>O<sup>+</sup> and OH<sup>−</sup>, so their concentrations are equal to {{val|1.00|e=-7|u=mol∙dm<sup>−3</sup>}} at 25 °C. A solution in which the H<sub>3</sub>O<sup>+</sup> and OH<sup>−</sup> concentrations equal each other is considered a '''neutral''' solution. In general, the pH of the neutral point is numerically equal to pK<sub>w</sub>/2.
| |
| | |
| Pure water is neutral, but most water samples contain impurities. If an impurity is an [[acid]] or [[base (chemistry)|base]] this will affect the concentrations of hydronium ion and hydoxide ion. Water samples which are exposed to air will absorb the acid [[carbon dioxide]] and the concentration of H<sub>3</sub>O<sup>+</sup> will increase. The concentration of OH<sup>−</sup> will decrease in such a way that the product [H<sub>3</sub>O<sup>+</sup>][OH<sup>−</sup>] remains constant for fixed temperature and pressure.
| |
| | |
| ==See also==
| |
| {{Portal|Water}}
| |
| *[[Chemical equilibrium]]
| |
| *[[Acid–base reaction]]
| |
| *[[Standard hydrogen electrode]]
| |
| | |
| ==References==
| |
| <references/>
| |
| | |
| ==External links==
| |
| * [http://www.vias.org/genchem/acidbase_equ_12591_04.html General Chemistry] – Autoionization of Water
| |
| | |
| {{Chemical equilibria}}
| |
| | |
| {{DEFAULTSORT:Self-Ionization Of Water}}
| |
| [[Category:Water chemistry]]
| |
| [[Category:Equilibrium chemistry]]
| |
| [[Category:Acid-base chemistry|Water]]
| |
| | |
| [[de:Protolyse#Autoprotolyse]]
| |
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