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<p><font face="serif">Here is some help for doing the calculations
related to the thermochemistry lab.</font></p>
<p><font face="serif"><b>REACTION 1</b><br>
</font></p>
<p><font face="serif">In the first reaction you did you combined 2
grams (you need to use your actual mass) of NaOH (s) with 50.0
ml of water. The water has a density of 1 g/ml so the mass of
the water was 50.0 g. Therefore the TOTAL mass of your
solution was 52 g.</font></p>
<p><font face="serif">Remember -- this is now a solution of NaOH
(aq) so you need to use the specific heat capacity provided on
the report form 3.93 J/g°C.</font></p>
<p><font face="serif">To calculate the heat in this case...</font></p>
<p><font face="serif"><img alt="$q = mc_s\DeltaT =
(52.00)(3.93)\Delta T$" style="vertical-align: middle;"
src="cid:part1.E4B96827.077CBC9A@mercer.edu"></font></p>
<p><font face="serif">Once you compute the heat, you need to convert
that to an enthalpy by dividing through by the moles of NaOH
reacted.</font></p>
<p><font face="serif">Moles of NaOH = (2.00 g) / (40.00 g/mol) =
0.0500<br>
</font></p>
<p><font face="serif">where 40.00 is the molar mass of NaOH.
Remember to use YOUR MASS of NaOH in your calculations.</font></p>
<p><font face="serif">The Enthalpy in J/mol is then <img
alt="$q/0.0500$" style="vertical-align: middle;"
src="cid:part2.BDE625B9.2A53BCDC@mercer.edu">. It is
exothermic, so the sign should be NEGATIVE.</font></p>
<p><font face="serif"><br>
</font></p>
<p><b><font face="serif">REACTION 2</font></b></p>
<p><font face="serif">In this reaction you are mixing 50.0 ml of 1 M
NaOH with 50.0 ml of 1 M. This will make 100.0 ml of solution
and we are told on the report form that the density of this
solution is 1.02 g/ml and that it has a specific heat of 4.02 </font><font
face="serif"><font face="serif">J/g°C.</font></font></p>
<p><font face="serif"><font face="serif">In this case the heat is</font></font></p>
<img alt="\documentclass{article}
\usepackage[utf8x]{inputenc}
\pagestyle{empty}
\begin{document}
q = mc_s\Delta T = (50.0 + 50.0)(1.02)(4.02) \Delta T%this is
where your LaTeX expression goes
\end{document}
" title="\documentclass{article}
\usepackage[utf8x]{inputenc}
\pagestyle{empty}
\begin{document}
q = mc_s\Delta T = (50.0 + 50.0)(1.02)(4.02) \Delta T%this is
where your LaTeX expression goes
\end{document}
" style="vertical-align: middle;"
src="cid:part3.0D9FFDD2.1D2A66B6@mercer.edu">
<p><font face="serif"><font face="serif"><font face="serif">Where
the (50.0 + 50.0)(1.02) terms convert the volume to a mass.
<br>
</font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif">As
before, I need to convert the heat to an enthalpy. In this
case to find the moles of NaOH I multiply the volume of NaOH
by the molarity of NaOH.</font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif">Moles
NaOH = (1.00 M)(0.050 L) = 0.050 moles</font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif">So
again, the Enthalpy </font></font></font><font face="serif"><font
face="serif"><font face="serif"><font face="serif">in J/mol is
<img alt="$q/0.0500$" style="vertical-align: middle;"
src="cid:part2.BDE625B9.2A53BCDC@mercer.edu">. It is
exothermic, so the sign should be NEGATIVE.</font></font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif"><font
face="serif"><br>
</font></font></font></font></p>
<p><b><font face="serif"><font face="serif"><font face="serif"><font
face="serif">REACTION 3</font></font></font></font></b></p>
<p><font face="serif"><font face="serif"><font face="serif"><font
face="serif">In this reaction we are doing essentially
what we did in REACTION 2, except that we are using solid
NaOH. We dilute the HCl solution up to 100 ml initially
because we want to have, after the addition of the NaOH, a
solution with approximately the same density and specific
heat capacity as we had in REACTION 2. In this
particular case the mass of the solution will be 102.0
grams; this is the 100 grams of HCl solution plus the mass
of the massed NaOH solid, so make sure you use your value
for the mass of the NaOH. To calculate the heat:</font></font></font></font></p>
<p><font face="serif"><font face="serif"><img
alt="\documentclass{article}
\usepackage[utf8x]{inputenc}
\pagestyle{empty}
\begin{document}
q = mc_s\DeltaT = (102.0)(1.02)(4.02)\Delta T%this is where
your LaTeX expression goes
\end{document}
" title="\documentclass{article}
\usepackage[utf8x]{inputenc}
\pagestyle{empty}
\begin{document}
q = mc_s\DeltaT = (102.0)(1.02)(4.02)\Delta T%this is where
your LaTeX expression goes
\end{document}
" style="vertical-align: middle;"
src="cid:part5.A82BBFE2.92FD9B0C@mercer.edu"></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif">And to
compute the enthalpy we need again the moles of NaOH (which
should be just like the process we followed in step one
where we had solid NaOH).</font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif"><font
face="serif">Moles of NaOH = (2.00 g) / (40.00 g/mol) =
0.0500</font></font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif"><font
face="serif"><font face="serif">The Enthalpy in J/mol is
then <img alt="$q/0.0500$" style="vertical-align:
middle;" src="cid:part2.BDE625B9.2A53BCDC@mercer.edu">.
It is exothermic, so the sign should be NEGATIVE.</font></font></font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif"><br>
</font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif">Convert
ALL of your enthalpies to kJ/mol and fill out the
appropriate places on the chart.</font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif">Let me
know if you have questions!!!!<br>
</font></font></font></p>
<p><font face="serif"><font face="serif"><font face="serif"><font
face="serif"><br>
</font></font></font></font></p>
<p><font face="serif"></font><br>
</p>
<pre class="moz-signature" cols="72">--
Andrew J. Pounds, Ph.D. (<a class="moz-txt-link-abbreviated" href="mailto:pounds_aj@mercer.edu">pounds_aj@mercer.edu</a>)
Professor of Chemistry and Computer Science
Director of the Computational Science Program
Mercer University, Macon, GA 31207 (478) 301-5627
</pre>
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