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The standard enthalpies of formation of ions in aqueous solutions are obtained by arbitrarily assigning a value of zero to $\mathrm{H}^{+}$ ions; that is, $\Delta H_{\mathrm{f}}^{\mathrm{o}}\left[\mathrm{H}^{+}(a q)\right]=0.$ (a) For the following reaction $$\begin{aligned}&\mathrm{HCl}(g) \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \mathrm{H}^{+}(a q)+\mathrm{Cl}^{-}(a q)\\&\Delta H^{\circ}=-74.9 \mathrm{kJ} / \mathrm{mol}\end{aligned}$$calculate $\Delta H_{\mathrm{f}}^{\circ}$ for the $\mathrm{Cl}^{-}$ ions.(b) Given that $\Delta H_{\mathrm{f}}^{\circ}$ for $\mathrm{OH}^{-}$ ions is $-229.6 \mathrm{kJ} / \mathrm{mol}$ calculate the enthalpy of neutralization when 1 mole of a strong monoprotic acid (such as HCl) is titrated by 1 mole of a strong base (such as KOH) at $25^{\circ} \mathrm{C}$.

$a)-167 k J / m o l$$b)-56.2 k J / m o l$

Chemistry 101

Chapter 6

Thermochemistry

University of Central Florida

University of Kentucky

University of Toronto

Lectures

05:27

In chemistry, a chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Both reactants and products are involved in the chemical reactions.

06:42

In chemistry, energy is what is required to bring about a chemical reaction. The total energy of a system is the sum of the potential energy of its constituent particles and the kinetic energy of these particles. Chemical energy, also called bond energy, is the potential energy stored in the chemical bonds of a substance. Chemical energy is released when a bond is broken during chemical reactions.

05:21

The standard enthalpies of…

01:56

04:27

At $25^{\circ} \mathrm{C},…

So for this problem, given two parts and for part A were supposed to calculate the heat information for negative chloride ions given the following chemical reaction. So we know that the Delta H for this entire reaction his negative 74.9 killed Jules permit. We're going to take advantage of that to find the heat information from the negative core it on. So we know that we can express this Delta H as the following the heater formation, the negative chord ion both the heat information of H plus minus the heat information of the reactant since the only reaction in this case HCL. So we know from the problem. But the an AK wee solutions that the standard until p where the heat information for H plus is going to be zero so that take that out. We also know that the heat information for HCL is equal to negative 92 killer jewels per mole. And give that there's only one mole of HCL in this equation. We can re express the heat information in the native quarter on is the following. When we plug the numbers into this equation, we get the final answer or that the heat of formation of negative chloride is equal to negative. 167 Villagers. Permal. That is the answer to putting Part B. Now we have the neutralization equation, and we know that the heat information with O. H, the native of the hydroxide I own is equal to negative 202 199 negative 229 0.6 Killer jewels promote, and we're supposed to find the entropy of neutralization. So in this case, the entropy of neutralization is just the heat of reaction of the neutralization reaction. So we can just write that reaction as the following because that is the neutralization reaction for hydro Clark acid. So the important thing to note here, however, is that this isn't the final This this isn't that final that equation because there are some spectator ions, for example, both C L. Minus in Cape Wallace. Or expect tighter spectator ions so they can be eliminated. So the final or than that equation, it was just going to be age plus to still reach minus milled each to it. So from there we can just use this equation and find the heat of reaction and that could help us find the heat of neutralization. So once again, we know that the heat information for H plus zero So that isn't going to meet He needed in this problem. So the heat of neutralization going to be the heat information Reach tool liquid minus the heat of formation of the O. H. Minus ion and only plug those numbers in and there's only one roll of H 20 and O H minus. You know that the heat information for water is negative. 285.8 killed Jules per mil. Or and we know that the heat of formation for the negative for the hydroxide ion is negative. 200 29.6. So the two natives cancel up. Let me simply add 229 0.6 killed Germans. When we add those two together we get the heat of neutralization is negative. 56.2 killed Jules promote and that is the final answer

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