So there are several
sources of properties, thermodynamic
properties and for that matter transport properties
which we'll get to later. Clearly, you can go to the literature as painful
as this might be, but you have Google and Google Scholar and those
are relatively easy to use. A second source of information about
properties is experiments. I think most of us would
not do experiments, 40 and 50 years ago
there was a lot of experimental work going on determining thermodynamic
properties of substances. Nowadays, there's a lot
less of that primarily because calculations have
gotten so much better. You can carry out Ab Initio Calculations,
quantum calculations. It's hard to do if you're
just a working engineer, you're not likely to do that, but it's not impossible and
it is actually done quite frequently by physical chemists
and applied physicist. Then finally, there are empirical estimation methods and they are often good for
first approximation, sometimes surprisingly
good especially, if the molecule was a big one and there's no experimental data and it's very difficult to do
quantum calculations on it. It may be all you can do. So literature sources
of properties, you can just do as I mentioned, a Google search or
Google Scholar search. Google Scholar usually get you better results
than just Google. Then there's a large body
of data available in a couple of websites mainly, National Institute of
Standards or NIST databases, and I will look at
those databases now. So here is the opening page of the NIST Chemistry WebBook. This page is an entry to an amazing amount of information about
various molecules. One can search a variety of ways, you can search by the formula,
the chemical formula, or the name, two different
identifier systems but you can search by a reaction, an author perhaps that
studied that molecule. You can even input information
about the structure, and you can do property
based searches for example, you could search by
molecular weight. We'll search by formula here, and I'm just going to arbitrarily pick ethylene or ethene, C2H4, and I'll institute
the search like this. You'll get a list of long
molecules that are in the database that
have the formula C2H4 or where they have
a formula involving deuterium D. The
reason for this is that often in reactivity studies, chemists will often substitute
for a hydrogen and they'll substitute it to deuterium or a certain number of deuteriums. Because then if you
do mass spectrometry, you can distinguish
because deuterium has a different molecular
weight than hydrogen. In any event, we're
just interested in plain old ethylene or ethane depending on the
naming convention you choose. So I'll click on that and this is a general page of the
information that you can get. So it gives the formula
of the molecular weight. It gives standard
identifier so IUPAC is International Union and frankly Africa what
the rest of it is, and this is the nomenclature that describes this molecule. This is a nomenclature
that actually gives you the physical arrangement
of the molecule. You can actually download
that identifier. There's actually three
identifiers here. One of them is CAS which has a numbering system for molecules. Then it shows the
molecular structure, you can download this
as what's called a Mol file or a computed file and you can actually view it using Java or JavaScript. So I do not have them enabled in my browser
so it will not do that. Let's see if I have JavaScript. Yes, I do. So here's
an example of ethylene and this
is a cartoon form, it's called ball and stick. So each ball represents an atom and each stick represents a bond. So ethylene is C2H4. So the carbons are double bonded and the hydrogens
are single bonded. Okay. You can get
information from this. I'll go back here, I
noticed that you can get some information about the vibrational frequencies
of the molecule. So moving on down here, there's a whole ton
of information. This gives gas phase
thermochemistry data, it gives the heat of formation, and it gives specific heat, and it gives the entropy. If you recall, if you
have those things, you can get all of
the other properties, and usually it gives you, it might give you
multiple sources, for example, the specific heat. So this gives two
different sources, it often will give
you an equation using a series
representation curve fit, in other words, and there's
something called the Shomate equation which is often used. This is not the same by the way, it's the mass of formulation
which is in combustion, at least we usually use
the mass of formulation, but you can take
this data and you can do an isotope fit to it, and it'll give all the
references for these species. So that's one source of data. Another source of data is from Argonne
National Laboratories, and it's called the Active
Thermochemical Tables or ATCT. The way this works is you
go to thermochemical data, and there's various
versions of it. I just always go to the initial version
if I can get there. There we go, and it lists all of the molecules
that are in the database, but we can select one
and what we'll get is this molecule and we'll
get one close to it. So again, I'll do
ethene or ethylene, same thing, and here it is. But it also gives stuff that's
related to ethylene that's close to it or as deuterated etc. So here's ethylene and it gives the enthalpy
of formation, and if I click on it, I get a bit more detail, it gives the formula and
shows an image of it. Again, it gives the
enthalpy of formation, it gives the molecular weight, and gives their ID number, the act of thermochemical
data table identifier. It gives some information
about some of the reactions that
ethylene can undergo. Another approach to obtaining properties is something
called group additivity. This is essentially
the only thing that's available if
there's no data or no Ab initio calculations available for the
particular molecule that you're interested in. It's based on the concepts of functional groups that behave
in a similar fashion that was initially developed by Professor Sydney Benson of UCLA. The method works like this, every molecule is considered to be made up of several groups. So here's an example,
with iso-pentane. Iso-pentane is C5H1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. So C5H12, and the way the groups are
identified is by carbons. So this group on the
right-hand side, the center of the
group is C and what's attached to it is three
hydrogens and one carbon. So it's identified as C-H3C, and each add each heavy atom meaning an atom that isn't hydrogen is referred
to as a group. So groups are identified by the atoms they are attached to. Iso-pentane is also called methylbutane
or 2-methylbutane. So it's made up of
these three groups. Three carbon with three
hydrogens and a carbon, one carbon with two
hydrogens and two carbons, and one carbon with
hydrogen and three carbons, connected to three carbons. So there are tables
of group properties, and this is an
example of one here. So it lists the properties
for each of these groups. So you have a Delta H_f, the enthalpy of formation, you have the entropy and you have C_P for a range
of temperatures. So basically, you just
linearly add these up. So for Delta H_f, you have three of
the first group, one of the second group, and one of the third group. You just add them up, you multiply 3 times minus 10.08, which is Delta H_f
for the first group, 1 times minus 4.95 and
1 times minus 1.9, and that gives you minus
37.1 Kcals per Mole. Now, if you go and
look that up in the NIST database or in the ATCT of chemical tables you'll get up pretty close to
the same thing. It's almost that simple,
group additivity methods. There are corrections
for special situations, and for some groups, there isn't any data and so
the method can't be applied. However, there's a web based
resource provided by NIST, it's located at this
web address here. You would need to provide
a structure file but if you remember from what we just did with the NIST database, if you go in and select a
molecule within their database, you can download the
so-called Mol file for this, or you can draw it using
special drawing software. So you can get into
that and carry out a group additivity
method that there is. So what are your marching orders? If you need thermochemical
data for something, look for the data, look in the NIST web book or the ATCT of chemical tables
or search the literature. That's probably your first step. Second step, try
group additivity, and the third step
is call a chemists. Call somebody that really
knows their business here, and get them to help you. So that's it. Thanks very
much. Have a great day.