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<div class="moz-cite-prefix">On 10/12/21 8:55 PM,wrote:<br>
</div>
<blockquote type="cite"
cite="mid:8ec363d235ac414aab6dfd79d4b0073b@SA1PR01MB6528.prod.exchangelabs.com">
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<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
Hi Professor, </div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
I had a question regarding column two of the lab report which
reads "mass of solution". Were we supposed to measure the mass
of our solution in the calorimeter once all the reactants had
been added?</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
<br>
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<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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Thanks, </div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
Ellie</div>
</blockquote>
<p><font face="serif">I can do better than that! Here is some help
for doing the calculations related to the<br>
thermochemistry lab.<br>
<br>
*REACTION 2*<br>
<br>
In the first reaction you did you combined 2 grams (you need to
use your<br>
actual mass) of NaOH (s) with 50.0 ml of water. The water has a
density<br>
of 1 g/ml so the mass of the water was 50.0 g. Therefore the
TOTAL<br>
mass of your solution was 52 g.<br>
<br>
Remember -- this is now a solution of NaOH (aq) so you need to
use the<br>
specific heat capacity provided on the report form 3.93 J/g°C.<br>
<br>
To calculate the heat in this case...<br>
</font></p>
<p><br>
</p>
<p><font face="serif"><math
xmlns="http://www.w3.org/1998/Math/MathML"><semantics><font
size="+1"><mrow><mi>q</mi><mo>=</mo><mi>m</mi><msub><mi>c</mi><mi>s</mi></msub><mi
mathvariant="normal">Δ</mi><mi>T</mi><mo>=</mo><mo
stretchy="false">(</mo><mn>52.00</mn><mo
stretchy="false">)</mo><mo stretchy="false">(</mo><mn>3.93</mn><mo
stretchy="false">)</mo><mi mathvariant="normal">Δ</mi><mi>T</mi></mrow></font></semantics></math><br>
</font></p>
<p><font face="serif"><br>
<br>
Once you compute the heat, you need to convert that to an
enthalpy by<br>
dividing through by the moles of NaOH reacted.<br>
<br>
Moles of NaOH = (2.00 g) / (40.00 g/mol) = 0.0500<br>
<br>
where 40.00 is the molar mass of NaOH. Remember to use YOUR
MASS of<br>
NaOH in your calculations.<br>
<br>
The Enthalpy in J/mol is then
<math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>q</mi><mo>/</mo><mn>0.0500</mn></mrow><annotation
encoding="TeX">q/0.0500 </annotation></semantics></math>.
It is exothermic, so the<br>
sign should be NEGATIVE.<br>
<br>
<br>
*REACTION 3*<br>
<br>
In this reaction you are mixing 50.0 ml of 1 M NaOH with 50.0 ml
of 1 M.<br>
This will make 100.0 ml of solution and we are told on the
report form<br>
that the density of this solution is 1.02 g/ml and that it has a<br>
specific heat of 4.02 J/g°C.<br>
<br>
In this case the heat is<br>
</font></p>
<p><br>
</p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>q</mi><mo>=</mo><mi>m</mi><msub><mi>c</mi><mi>s</mi></msub><mi
mathvariant="normal">Δ</mi><mi>T</mi><mo>=</mo><mo
stretchy="false">(</mo><mn>50.0</mn><mo>+</mo><mn>50.0</mn><mo
stretchy="false">)</mo><mo stretchy="false">(</mo><mn>1.02</mn><mo
stretchy="false">)</mo><mo stretchy="false">(</mo><mn>4.02</mn><mo
stretchy="false">)</mo><mi mathvariant="normal">Δ</mi><mi>T</mi></mrow><annotation
encoding="TeX">q = mc_s\Delta T = (50.0 + 50.0)(1.02)(4.02)
\Delta
T</annotation></semantics></math><br>
</p>
<p><br>
</p>
<p><font face="serif">Where the (50.0 + 50.0)(1.02) terms convert
the volume to a mass. <br>
<br>
As before, I need to convert the heat to an enthalpy. In this
case to<br>
find the moles of NaOH I multiply the volume of NaOH by the
molarity of<br>
NaOH.<br>
<br>
Moles NaOH = (1.00 M)(0.050 L) = 0.050 moles<br>
<br>
So again, the Enthalpy in J/mol is
<math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>q</mi><mo>/</mo><mn>0.0500</mn></mrow><annotation
encoding="TeX">q/0.0500</annotation></semantics></math>.
It is exothermic, so<br>
the sign should be NEGATIVE.<br>
<br>
<br>
*REACTION 4*<br>
<br>
In this reaction we are doing essentially what we did in
REACTION 3,<br>
except that we are using solid NaOH. We dilute the HCl
solution up to<br>
100 ml initially because we want to have, after the addition of
the<br>
NaOH, a solution with approximately the same density and
specific heat<br>
capacity as we had in REACTION 3. In this particular case the
mass of<br>
the solution will be 102.0 grams; this is the 100 grams of HCl
solution<br>
plus the mass of the massed NaOH solid, so make sure you use
your value<br>
for the mass of the NaOH. To calculate the heat:<br>
<br>
</font></p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>q</mi><mo>=</mo><mi>m</mi><msub><mi>c</mi><mi>s</mi></msub><mi
mathvariant="normal">Δ</mi><mi>T</mi><mo>=</mo><mo
stretchy="false">(</mo><mn>102.0</mn><mo stretchy="false">)</mo><mo
stretchy="false">(</mo><mn>1.02</mn><mo stretchy="false">)</mo><mo
stretchy="false">(</mo><mn>4.02</mn><mo stretchy="false">)</mo><mi
mathvariant="normal">Δ</mi><mi>T</mi></mrow><annotation
encoding="TeX">q = mc_s\DeltaT = (102.0)(1.02)(4.02)\Delta T</annotation></semantics></math><br>
</p>
<p><font face="serif"><br>
</font></p>
<p><font face="serif">And to compute the enthalpy we need again the
moles of NaOH (which<br>
should be just like the process we followed in step one where we
had<br>
solid NaOH).<br>
<br>
Moles of NaOH = (2.00 g) / (40.00 g/mol) = 0.0500<br>
<br>
The Enthalpy in J/mol is then
<math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>q</mi><mo>/</mo><mn>0.0500</mn></mrow><annotation
encoding="TeX">q/0.0500</annotation></semantics></math>.
It is exothermic, so the<br>
sign should be NEGATIVE.<br>
<br>
<br>
Convert ALL of your enthalpies to kJ/mol and fill out the
appropriate<br>
places on the chart.<br>
<br>
Let me know if you have questions!!!!<br>
</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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