. Two Liters of pure water \'split\' into H2 and O2 gas at 25 C and 1 bar pressu

Question

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Two Liters of pure water 'split' into H2 and O2 gas at 25 C and 1 bar pressure a) calculate t the delta U, delta H, delta S surroundings, Delta S system delta G of the reaction b) is it spontaneous at 25 C and 1 bar explain C) I if you are asked to suggest a temperature at which the reaction will be spontaneous what would that temperature be (you may assume P, Delta H of reaction and Delta S of reaction are constant the process)

Please help,I have the exam tomorrow and I've read the chapters and I don't know which formula to use, please tell me what you use and why

Explanation / Answer

Ans.)

Enthalpy is defined: H=U+PV which means that (at constant pressure) H=U+PV, or rewritten to be U=HPV. U=q+w at constant pressure becomes, U=qPPV, which means that H=qP
U=q+w at constant volume becomes, U=qV

Gibb's Free Energy

The Gibb's Free Energy (G) is another state function that is defined from 3 others: G=HTS. When we hold temperature and pressure constant we get:

G=HTS

We typically are getting the X's in the above equation from Standard Thermodynamic Data Tables like you have in Appendix 4 in your textbook. If you are at standard state you add the superscript "°"'s to the terms:

G=HTS

Of course this means that the temperature must be 25°C or 298.15 K in the above equation. You can also show through a simple proof that G (a system state function) is equal to T;S univ. So we can now use G as our indicator of spontaneity for a reaction or process.

Definition of Thermodynamic equilibrium: G=0

Also, we can assume that plain ol' G (non-standard conditions) is approximately equal to the adjusted standard values for H and S via temperature:

GHTS

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