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### Topic: enthalpy of reaction in Phosphoric acid equilibrium  (Read 1395 times)

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#### vanthoffreacenth

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##### enthalpy of reaction in Phosphoric acid equilibrium
« on: June 06, 2023, 04:52:59 AM »
Hi,

I'm currently working through independent research and decided to do an experiment pertaining to attaining a value for change in keq in chemical equilibrium given a change in temperature. This abides by the Van't Hoff theorem, and when putting my data (15000 points of data averaged under each degree over a 40CÂș span) and got a 0.998 R^2 coefficient.

I did my experiment by measuring 2.9M phosphoric acid dissolution through pH and then attaining keq through change in pH.

At this point, I want to ascertain the level of accuracy of my data but after searching for hours I can't find a single value for enthalpy of reaction for phosphoric acid and can't calculate it as there's no value for enthalpy of formation of H2PO4-.

Can anyone help me out? I feel so stuck and I'm on a rapidly approaching deadline.

Cheers, Vant

#### Hunter2

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##### Re: enthalpy of reaction in Phosphoric acid equilibrium
« Reply #1 on: June 06, 2023, 07:11:20 AM »
If you can't find use the law of Hess
Use Standard enthalpies.

How do I calculate the standard enthalpy of formation H3PO4 (aq) + NaOH (aq) -> NaH2PO4 (aq) + H2O (l) Known standard Enthalpies of Formation are H3PO4 (aq): -1288.34 kJ/mole NaH2PO4 (aq): -1536.4 kJ/mole H2O (l): -285.840 kJ/mole NaOH (aq): -469.15 kJ/mole