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<div class="moz-cite-prefix">On 6/8/19 12:53 PM, wrote:<br>
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<blockquote type="cite"
cite="mid:0f63395600254d78b68384602e25c594@MN2PR01MB5550.prod.exchangelabs.com">
<pre class="moz-quote-pre" wrap="">Hello Dr. Pounds,
I am a little confused with this problem and how they are getting some of the numbers, the problem says:
A quantity of 2.00 x 10 ^2 mL of 0.862 M HCl is mixed with 2.00 x 10 ^ 2 mL of 0.431 M Ba(OH) 2 in a constant pressure calorimeter of negligible heat capacity. The initial temperature of the HCL and BaOH2 solution is the same at 20.48°C. For this process H+ (aq) +OH- (aq) ———> H2O (l) the heat neutralization is-56.2 kJ/mol. What is the final temperature of the mixed solution? Assume the specific heat of the solution is the same as that for pure water.
In order to complete this problem I need to find grams, because they have me everything else. Okay, so I know the first thing I am supposed to do is make a balanced equation and then I am supposed to find the limiting reactant of either BaOH or HCL. I looked for the limiting reactant of HCl, and there appears to be no limiting reactant. After that, I am supposed to calculate the heat. However I am confused, because when I am finding OH-, how do I know that One mole of OH is equal to -56.2 kJ, because the problem doesn’t say that.
Also, since I am finding grams and they do not give it to me, do I assume that the grams of HCL and BaOH is 1.00 g ?
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<p><br>
</p>
<p>You do not need to find the grams because they have given you the
volumes and molarities -- remember molarity multiplied by volume
is moles.</p>
<p>Note also that the barium hydroxide is providing TWO MOLES of
hydroxide to the reaction for each mole of barium hydroxide -- so
in this case the molarity of hydroxide is effectively double what
is given (rather than 0.431 M, it is 0.862 M).</p>
<p>Now, according to the thermodynamic data given, the ENTHALPY OF
NEUTRALIZATION is for ONE MOLE of H+ reacting with ONE MOLE of OH-
-- which is -56.2 kJ (per mole, that is provided in the problem
statement).<br>
</p>
<p>So - use the molarities and volumes to determine the number of
moles reacted; then use that value and the molar enthalpy of
neutralization to determine the heat (q) evolved.</p>
<p>There is no need to assume 1.00 g of HCl and BaOH -- again, all
the information about the moles reacting in this case is tied up
in the molarity and volume.</p>
<p>They tell you to assume that the specific heat for the solution
is that of pure water (4.184 J/deg.g) and you can also therefore
assume that the density of water is 1.00 g/ml. The solution is
made by mixing 200 ml of HCl with 200 ml of Ba(Cl)2 -- which would
be a volume of 400 ml -- and based on the density of water, it
should have a mass of 400 g.</p>
<p>Set up <img alt="$q=mc_s \Delta T$" style="vertical-align:
middle;" src="cid:part1.E69BE729.CE357686@mercer.edu">, plug in
all your known values and determine the final temperature.</p>
<p><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
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