Subject: Exp 6 and using Excel for Exp 6

Some students often ask questions about heat capacity
and the equations to use for exp 6.  You should read
chapter 5 concerning the sections about delta(H), Hess's
Law and calorimetry.

The book discusses the relationship between heat, mass,
specific heat and temperature change for a substance.  The
eqn that relates these is given in the lab manual as well.
This eqn is,

	 q =     m  *    s     *  delta(T)

	heat = mass * sp. heat * temp chg.

Sometimes instead of "s" a "c" (lower case) or C_s is used
for specific heat.  The eqn not shown in the textbook (but
it is discussed in the lab manual) is the more general
relationship,

	q = C * delta(T),

where "C" (upper case) is the heat capacity of a substance.
Heat capacity is an extensive quantity and depends on the
amount of material present.

Specific heat, "s", is the heat capacity per gram.  This
is an intensive quantity and doesn't depend on the amount
of material present.

Mass * sp. heat is heat capacity.

When you are using something that is not homogeneous
(not uniform) it doesn't have the same properties
throughout, such as sp. heat.  Thus you can't use sp. heat
and have to determine the heat capacity of that certain
object.  The styrofoam coffee cup (our cheap calorimeter)
is not uniform throughout and each one is different.  Thus,
in part A you are determining the heat capacity for the
specific coffee cup and lid you are using. This is why it's
important if you don't finish exp 6 you keep the coffee
cup and lid you are using.  Otherwise when you continue
exp 6 in another lab period you would have to do part A
again for the new coffee cup and lid.  It's also the reason
to be careful and not poke a hole in the cup or you will have
to do part A over again with a new cup and then repeat any part
of parts B or C you haven't finished with the new cup.

During your data collection you will be determining temps
at specific times.  You should have a table of time and
temp data for parts A, B and C.  You will use this data to
make the necessary graphs, like the figure on page 41 of the
lab manual. However, this graph is just a rough example.  You
should look at my example of a finished graph on my web
page as this gives a much better idea of what your finished
graph should look like.  Make sure you swirl the liquid in
the cup before each temp. reading to make sure the temperature
is equilibrated throughout the cup.


**** data manipulation and graphs ******

The following applies in general to graphing for exp 6,
whether using Excel or something like Excel.  I have
a few more specific instructions for using Excel for
Exp 6 at a subsequent link.  Do NOT graph by hand.

When you make your graphs it you should use the long edge
of the graph paper for the Temp (y-axis) and time (x-axis)
on the short edge of the graph paper.  The temp should be
more accurate than your time.  Spread things out so there's
a minimum of empty space.  You may need a small amount of
empty space at the top since you will be extrapolating
back to the line representing the time of addition.
If you can spread things out enough you may be able to gain
an extra digit (sig. fig.) for your temperatures (the Ti and
Tf).

Look at figure on page 41 in the manual for a general
idea of what the graph should look like.  This shows what
it should generally look like.  It does not have the proper
sig.  fig. on the axes and has a little too much empty space
at the bottom.  The more you can spread out your data
the better.  Your axes should have the correct number
of sig. fig. For most this will be 3 for temp (since you
could record the temp to one decimal place) and
probably 2 for the time (maybe 3 depending on how
carefully you measured the time).  Again, the finished
graph on my web page gives a much better idea of what your
finished graph should look like.

Make sure on your graph to clearly label the initial (Ti)
and final (Tf) temps you get by extrapolating back to the
line of addition.  When drawing the best-fit line for Ti
use the last few temperature points.  For the best-fit line
for Tf you want to use the first several points where the
temp. started to show a constant decrease.  Generally
speaking, your Tf should be higher than your highest temp.
reading, assuming you did things correctly when taking
the data.

You can use Excel for exp 6 but only to plot the points
using a scatter graph, not a line graph.  You should not
have it do a trend line.  You should have it draw lots of
gridlines and then you draw the lines for Ti, Tf and the
vertical line (time of addition) by inserting lines in
Excel.  Go to "Insert" and you'll find an option for adding
text, drawing lines, shapes, etc.

Your graphs should take up essentially the whole page with
one graph to a page.  Set your margins to zero in Excel.
Excel may complain about this for printing, ignore it. The
axes should be set up so your data points occupy most of the
space on the graph (no large empty areas - spread the data
points out).  You need to have a title and axes labels (with
proper units).  Your graph title needs to be descriptive of
what you are plotting.  You can see this in the the sample
graphs I have on my web pages (not the examples for this exp).
There the volume was graphed as a function of temp. (V vs. T)
so this was part of the title "Figure 1:  Volume vs.
Temperature for Part A".  You should do the same sort of
thing on your graphs.

When using Excel, don't make the font for these things so large
it takes up a lot of space.  A 12 point font will be big enough
for the labels, a 10 point font for the numbers on the axes
and 14 point for graph title is fine.  You should set your
margins around the graph to zero.  If Excel complains tell it
to ignore the complaint.  Get rid of the border around the
graph.

You do not need a legend for the data when there's only 1 set
of data plotted.  Excel will often put a legend by default.
Remove it for these graphs so the graph can spread out.

I have examples on how to do certain things using Excel for
exps 14 and 17.  You can look at these for some idea of how to
use Excel.  Remember, my examples for exp 14 and exp 17 are just 
examples.  I have not done everything you need to do when using
Excel for graphing. I've left some things off the examples of the
graphs (units, etc.).  You need to figure some of these things out
for yourself.  I also have some additional instructions for using
Excel for exp 6 at the "Using Excel for Exp 6" link.  You should
look at this even if you aren't using Excel to get an idea about
what the graphs should look like.

When done with your graphs transfer them to Word.  Do NOT scan
them or take a picture to include in the report.  There are
various ways to get a graph or table from Excel into Word.  The
easiest way is to copy the graph/table in Excel and paste it
into Word.

You can also look at my examples for the graphs.  The first
link is the graph w/o the lines.  The second graph shows the
time-of-addition line and the best fit lines for determining
Ti and Tf.

https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/exp6_partA_graph.pdf

https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/exp6_partA_finished.pdf


Dr. Zellmer