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2013-03-15T10:54:31Z

Bot: Migrating 2 interwiki links, now provided by Wikidata on d:q2898181

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	~~Hello~~. ~~Allow me introduce the writer~~. ~~Her title~~ is ~~Refugia Shryock~~. ~~Managing people~~ is ~~his occupation~~. ~~One~~ of the ~~issues she loves most~~ is to ~~read comics and she'll~~ be ~~starting something else alongside with it~~. ~~South Dakota~~ is ~~exactly where me~~ and ~~my spouse live~~ and ~~my family members loves it~~.<br><br>~~Feel free~~ to ~~surf~~ to ~~my page~~ [~~http~~://~~www~~.~~animecontent~~.~~com~~/~~blog~~/~~349119 http~~://~~www~~.~~animecontent~~.~~com~~/]		'''ICE chart''', or '''ICE box''' is a tabular system of keeping track of changing concentrations in an [[equilibrium reaction]]. '''ICE''' stands for "'''''I'''nitial, '''C'''hange, '''E'''quilibrium''".<ref>[http://www.youtube.com/user/genchemconcepts#p/a/u/5/LZtVQnILdrE General Chemistry Concepts - YouTube]</ref> It is used in chemistry to keep track of the changes in [[amount of substance]] of the reactants and also organize a set of conditions that one wants to solve with. Occasionally, the chemical '''r'''eaction is written at the top of the table, resulting in a '''RICE table'''.

			== Example ==
			To illustrate the processes, consider the case of dissolving a [[weak acid]], HA, in water. How can the [[pH]] be calculated? Note that in this example, we are assuming that the acid is not very weak, and that the concentration is not very dilute, so that the concentration of [OH<sup>-</sup>] ions can be neglected. This is equivalent to the assumption that the final pH will be below about 6 or so. See [[PH#Calculations of pH\|Calculations of pH]] for more details.

			First write down the equilibrium expression.
			:<math>HA \rightleftharpoons A^- + H^+</math>
			The columns of the table correspond to the three species in equilibrium.
			{\| class="wikitable" style="text-align:center"
			\|-
			! width=20 \|
			\| [HA] \|\| [A<sup>-</sup>] \|\| [H<sup>+</sup>]
			\|-
			! I
			\| C<sub>a</sub> \|\| 0 \|\| 0
			\|-
			! C
			\| -x \|\| +x \|\| +x
			\|-
			! E
			\| C<sub>a</sub> - x \|\| x \|\| x
			\|}

			The first row, labeled I, has the initial conditions: the ''nominal concentration'' of acid is C<sub>a</sub> and it is initially undissociated, so the concentrations of A<sup>-</sup> and H<sup>+</sup> are zero.

			The second row, labeled C, specifies the change that occurs during the reaction. When the acid dissociates, its concentration changes by an amount ''-x'', and the concentrations of A<sup>-</sup> and H<sup>+</sup> both change by an amount ''+x''. This follows from consideration of ''mass balance'' (the total number of each atom/molecule must remain the same) and ''charge balance'' (the sum of the electric charges before and after the reaction must be zero).

			Note that the coefficients in front of the "x" correlate to the mole ratios of the reactants to the product. For example, if the reaction equation had 2 H+ ions in the product, then the "change" for that cell would be "2x"

			The third row, labeled E, is the sum of the first two rows and shows the final concentrations of each species at equilibrium.

			It can be seen from the table that, at equilibrium, [H<sup>+</sup>] = x.

			To find ''x'', the equilibrium constant must be specified.

			:<math>K_a = \frac{[H^+][A^-]}{[HA]}</math>

			Substitute the concentrations with the values found in the last row of the ICE table.

			<math>K_a = \frac{x^2}{C_a - x}</math>

			<math>x^2 + K_a x - K_a C_a = 0</math>

			With specific values for C<sub>a</sub> and K<sub>a</sub> this [[quadratic equation]] can be solved for x. Assuming<ref>Strictly speaking pH is equal to -log<sub>10</sub>{H<sup>+</sup>} where {H<sup>+</sup>} is the [[Activity (chemistry)\|activity]] of the hydrogen ion. In dilute solution concentration is almost equal to activity</ref> that pH = -log<sub>10</sub>[H<sup>+</sup>] the pH can be calculated as pH = -log<sub>10</sub>x.

			If the degree of dissociation is quite small, C<sub>a</sub> ≫ x and the expression simplifies to
			:<math>K_a = \frac{x^2}{C_a}</math>
			and pH= 1/2( p''K''<sub>a</sub> - log C<sub>a</sub>). This approximate expression is good for p''K''<sub>a</sub> values larger than about 2 and concentrations high enough.

			== References ==
			<references/>

			[[Category:Equilibrium chemistry]]
			[[Category:Physical chemistry]]

en>Luckas-bot: robot Adding: es:TFNP

2010-07-12T21:07:05Z

robot Adding: es:TFNP

New page

Hello. Allow me introduce the writer. Her title is Refugia Shryock. Managing people is his occupation. One of the issues she loves most is to read comics and she'll be starting something else alongside with it. South Dakota is exactly where me and my spouse live and my family members loves it.<br><br>Feel free to surf to my page [http://www.animecontent.com/blog/349119 http://www.animecontent.com/]

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en>Addbot: Bot: Migrating 2 interwiki links, now provided by Wikidata on d:q2898181

en>Luckas-bot: robot Adding: es:TFNP