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From the following data, calculate the heat of solution for KI: $$\begin{array}{ccccc} & \mathrm{NaCl} & \mathrm{NaI} & \mathrm{KCl} & \mathrm{KI} \\\hline \text { Lattice energy } & 788 & 686 & 699 & 632 \\(\mathrm{kJ} / \mathrm{mol}) & & & & \\\begin{array}{c}\text { Heat of solution } \\(\mathrm{kJ} / \mathrm{mol})\end{array} & 4.0 & -5.1 & 17.2 & ? \\\hline\end{array}$$

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$43 \mathrm{kJ} / \mathrm{mol}$

Chemistry 101

Chapter 6

Thermochemistry

Rice University

University of Kentucky

Brown University

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.

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we're going to be solving for heat of solution for potassium iodide. Based on the data on this table. If you'll take a look at what we're provided here, we have lattice energy and the heats of solution. And we've got lattice energy for both sodium chloride and heats of solution for sodium chloride. We've got lattice energy and heat of solution for any I sodium iodide and for potassium chloride for K I, potassium iodide, we simply have the lattice energy, and we need to find the heat of solution. Okay, so we're gonna use the equation, the heat of solution. I mean, with this up a little bit. So I have room to write it all. The heat of solution is equal to the sum of lattice energy, plus the heat of hydration. We're gonna be solving for latte for heat of hydration, and we will be given these two values. So let's do each of the three calculations for N A. C. L and I I and K C l. And again, this one is pretty easy to do here. Um, we're gonna have to rearrange this to get the hydration. So our delta H for H Y D is going to equal the lattice energy, which is 4.0. And this will be minus the, um 7 88 which will give us 7 84 kill a Jules per mole. And for the second in a I, the heat of hydration will be negative. 5.1 minus 6 86 And that will give us negative 6 91 And they should have been negative. Negative 6 91 0.1 killer jewels per mole. And lastly, our heat of hydration for K. C. L is 17.2 minus 6 99 and that will be negative. 6 81 0.8. Kill a Jules per mole. Okay, so these values will be using for our next calculations. Now, what I'm trying to get here is potassium iodide. I want to get potassium iodide, and I'm going to use the equations for an A C L in a I and K C l. And each of these breaks down into the format of the metal ion in the gaseous phase. Plus the an ion in the gaseous phase produces the mental and I in in the quickest phase, plus the an ion in the quickest face. So each one of these three breaks down into this format. This is the equation that I want to get. So I'm going to use these three and with the heats that we that heats of hydration that we calculate on the previous page in order to get this final equation And let's start with the K C L. Because I've got, um, the K and the K. I need that in my final, I'm going to start with the exact equation. And if you look at this equation for the K C L, I've got the metal in the eye, Ana and I on the gaseous phase and then the metal in the anti on in the quickest phase, my delta h for this will be exactly as it was written on the previous page for the K C. L. And that was negative. 6 81 k c l 6 81.8 kill a Jules per mole. Okay, so that's my first equation, and it doesn't really matter what I'm going to do. The n a c l next. So I'm gonna do the any an a c l next because I want my chlorides, these two chlorides. My goal is to going to get these two to cancel out. So let's go ahead and use our sodium chloride. And I'll make this one, um, purple and I want my c l minus g in my n a plus g on this side and my n a my a quiz and my c l a quiz on this side. Now look what I can cross out and cross out my c l a quiz and my seal gases. And then last but not least, let's use our 30 equation the any I And let's see what I have got a better put my heat on this one. Um, my delta h for this one will be Since I flipped that equation, I'm going to have to flip this so it will be a positive and a sale. Positive. 7 84 0.0. Kill a Jules per mall. So now I have a positive 7 84 have a negative 6 81 And then last but not least, I'm gonna use my potassium iodide. Excuse me, my sodium iodide, and that one is going to be left as is. We're not gonna flip that one and you'll see why in a moment. And my delta h for this one is going to be the same. So n a I was negative. 6 91.1 killer jewels per mole. Okay, so now let's continue crossing out. I can cross out my in a plus and I can cross out my any plus us this way And that will leave me And I'm going to highlight thes that leaves make a I And that corresponds to these two and Equus and a quiz. There we go. So now I am going to go to the next page for this. The three values that we'd written down for those equations were flips. Switch back to my pen were negative. Let me do this in the same order. Let me go back. So I had negative 6 81.8 killer jewels per mall. That was from my k C l. And then I had positive 784.0 killer jewels per mole. And lastly, I had negative 6 91.1 killed Jules per mole. Add these together and we get negative. 5 88.9 killer jewels per mole so that we're not quite done yet. We're very close. Um, now we're gonna go back to our original calculation here. I'm gonna go back couple pages, Then I'll come up here again. We were given our lattice energy of 6 32 Let's see. And let's remember that our heat of solution I'm going to write this up here. Our heat of solution is legal to our lattice energy, which was 632 killer jewels per mole, plus our heat of hydration, which is right here, plus a negative 5 88.9 killer jewels per mole. Add these together and we get 43 killer jewels per mole. And that is the value in the table that we were looking for. So the value that we're looking for right here is 43.0 killer jewels per mole. There it is. 43 killer jewels promote

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