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[OLD] Temperature change


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From: Henry Kerfoot

Subject: temperature change

I am trying to evaluate the potential temperature change in unsaturated materials due to reactions. I have a system I wish to model, but I cannot seem to get a temperature increase from reactions that I think should give one. I have tried modeling the oxidation of pyrite and failed. I have been able to get a temperature increase when I use T initial = 15, reactants and have a large amount of reactants present (i.e., kg of silica) with a heat capacity of 0.2. My question is this: There is an 'isothermal' command, implying that computed temperature variations from chemical reactions are possible. What command is used to allow temperature changes from reactions? Just the default T = x?

 

From: Craig Bethke

Subject: RE: temperature change

Almost all geochemical calculations are formulated in terms of the Gibb's free energy, assuming that temperature and pressure are controlled by the environment of the system of interest. The equilibrium constants in the various GWB databases are transformations of the Gibb's free energy. As such, in tracing a reaction path with React, you are assuming that whatever heat energy is liberated by the enthalpy change of reaction is simply conducted into the environment. To model your situation, I suggest you perform the following steps:

1) Use React to discover the overall chemical reaction occurring in the system.

2) Calculate from standard tables the enthalpy change of reaction corresponding to the overall reaction.

3) Multiply this value by the number of moles of reaction progress observed to find the number of joules of heat energy added to the system, then divide this number by the system's overall heat capacity to get the temperature increase expected.

4) Rerun React as a polythermal simulation in which the final temperature is the initial temperature plus the predicted temperature increase.

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