Shomate coefficients for n-octane

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In summary, the speaker is looking for coefficients to use with the Shomate equation for n-octane (C8H18) but has been unable to find any. The NIST Webbook lists gas phase thermochemistry data but does not include Shomate coefficients for n-octane. The speaker is considering extrapolating enthalpy figures using Cp data from the NIST entry, but is unsure how to handle entropy at other temperatures. They are wondering if it is possible to properly model Cp/H/S for octane using the Shomate equation. Another person suggests that the data may not have been measured and the speaker may need to use extrapolated values from other compounds. The speaker acknowledges this and will do their best with
  • #1
manderson99
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Hello! I've been looking for coefficients to use with the Shomate equation for n-octane (C8H18), but I have been unable to find any. The NIST Webbook lists some gas phase thermochemistry data:

http://webbook.nist.gov/cgi/cbook.cgi?ID=C111659&Mask=1#Thermo-Gas

but it omits the Shomate coefficients that are present for some other compounds (methane, for example). I could extrapolate enthalpy figures using the Cp data included in the NIST entry, but I'd be at a loss as to what to do about entropy at anything but ATP.

It could be that one can't model Cp/H/S properly for octane using the Shomate equation, though I'm too ignorant to know whether or not that is the case.

So, can anyone help clear up this matter for me? Thanks!
 
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  • #2
You are probably looking at the price of data; i.e., it's not been measured. You might be able to "kluge" together a set from extrapolation of the pentane and hexane values that are in the tables plus a little "Kentucky windage."
 
  • #3
D'oh! Oh well, thanks for letting me know. I'll do my best with what's available.
 

1. What are Shomate coefficients for n-octane?

Shomate coefficients for n-octane are a set of thermodynamic data used to calculate the heat capacity, enthalpy, entropy, and other thermodynamic properties of n-octane at different temperatures. They are derived from experimental data and are used in thermodynamic calculations for various chemical reactions.

2. How are Shomate coefficients for n-octane determined?

Shomate coefficients for n-octane are determined through experimental measurements of heat capacity at different temperatures and pressures. These data are then fitted to a mathematical equation called the Shomate equation, which gives the values of the coefficients for n-octane.

3. Why are Shomate coefficients important for n-octane?

Shomate coefficients are important for n-octane because they allow for accurate calculations of thermodynamic properties, which are essential for understanding and predicting the behavior of n-octane in various chemical reactions. They also provide a standardized set of data that can be used by scientists and engineers in their research and design processes.

4. What are the units of Shomate coefficients for n-octane?

Shomate coefficients for n-octane are typically expressed in units of Joules per mole Kelvin (J/mol*K) for heat capacity and Joules per mole (J/mol) for enthalpy and entropy. However, the units may vary depending on the specific Shomate equation used and the source of the data.

5. Can Shomate coefficients for n-octane be used for other compounds?

No, Shomate coefficients for n-octane are specific to n-octane and cannot be used for other compounds. Each compound has its own unique set of Shomate coefficients, which are determined based on its molecular structure and experimental data. However, similar methods and equations can be used to calculate Shomate coefficients for other compounds.

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