thermo question

[Aurora09]

hey all, just a quick question on thermo properties:

does enthalpy, internal energy, specific value and entropy of a material all change with composition?

 

[Audi Driver P.E.]

The short answer is yes. The longer answer is, of course, it sort of depends. First of all, what do you mean by change with composition? Do you mean, for example 304 stainless steel vs. 316? Do you mean water but with a drop of alcohol in it?

 

[Pass the PE Exam]

@Aurora09, when you say composition are you, by any chance, referring to mass and therefore intensive/extensive properties? An intensive property is independent of mass, and an extensive property varies directly with mass.

Temperature, pressure, specific volume (specific, meaning per unit mass), density, specific internal energy, specific enthalpy, and specific entropy are all intensive properties.

Correspondingly, mass, volume, internal energy, enthalpy, and entropy are extensive properties.

I hope this answers your question. If not, can you please clarify what you mean by "composition"?

 

[Steve Beck]

Overall!!! we can say "Yes". 

• Internal energy is the 'intrinsic' energy of some system, can be measured with reference to something within the system, e.g. chemical bonds, vibrational energy states, etc.
  
• Enthalpy change is the heat (i.e. energy transferred due to temperature difference) change at constant pressure due to some chemical process.