Choosing a Reference State (Example)

[@sfindaa8523]

Thank youuuuu! Thank you so much. I had no idea what was going on in class!

[@SomeOne-or7ut]

how did she got delta H(vab) on 5:52, is it straight from a table and if that was so which table?

[@nikitajain4484]

Hi, for H1 what did you put in for Cp because I didn't get -2.96 for the integral, I got something else

[@dianaantillon1984]

How did you find the cp values?

[@minjinseo3681]

Why didn't you convert the temperature into Kelvin in 5:22 in the second integral part? The phase there was already in liquid and not anymore in gas phase. Still thanks for the video, have a great day :)

[@LearnChemE]

You are correct, however depending on the property table you look up, the heat capacities can either be in the form of Celsius or kelvin and since we are just showing how to set up the integral, it's not necessary to convert. It would still be the same temperature range regardless.

[@minjinseo3681]

Oh I see :) Thank you very much :)

[@alinaizi]

How did you know that the enthalpy is zero when choosing the ref at 60 deg C? and why 60 deg is better than the others?

[@LearnChemE]

Good question! By definition, when you chose a reference state the conditions at which you chose the reference state to be have an enthaply of zero. To give another example, the standard reference state for a lot of thermodynamic data is atomic species at 25 deg C and 1 bar pressure. If a component exists at these conditions, the enthaply is zero. In this problem, the reference state of benzene and toluene vapor at 60 deg C is chosen because it allows all of the initial enthalpies to be set to zero. You could easily chose either of the other two state described in the screencast an get the same answer. Does that sufficiently answer your question?

[@alinaizi]

+LearnChemE thank you so much I wish I could transfer to your school (MSU Student)

[@obakengmoletsane7643]

nice