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From the following heats of combustion, $$\begin{array}{c} \mathrm{CH}_{3} \mathrm{OH}(l)+\frac{3}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l) \\ \Delta H_{\mathrm{rxn}}^{\circ}=-726.4 \mathrm{kJ} / \mathrm{mol} \\\mathrm{C}(\mathrm{graphite})+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) \\\Delta H_{\mathrm{rxn}}^{\circ}=-393.5 \mathrm{kJ} / \mathrm{mol} \\\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l) \\\Delta H_{\mathrm{rxn}}^{\circ}=-285.8 \mathrm{kJ} / \mathrm{mol}\end{array}$$calculate the enthalpy of formation of methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$ from its elements: $\mathrm{C}(\text { graphite })+2 \mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{OH}(l).$

$-238.7 k J / m o l$

Chemistry 101

Chapter 6

Thermochemistry

Carleton College

University of Central Florida

University of Maryland - University College

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.

04:10

From the following heats o…

04:11

From the following data, $…

04:14

The standard molar heats o…

02:08

Calculate the standard ent…

um, we're going to be applying has his lock make sure my screens on. So here's what's gonna happen, and I'll start this on the next page. We're going to be given three equations on. They're going to be thermal chemical equations. They'll be, um, it's not very well written. They'll be thermal chemical equations so they will have a heat term, will be given a desired our target equation. And then we're going to rearrange and combine three equations to get the target. So that's our goal. Let's begin. Okay. I took the liberty of writing these down, and I want to make sure again my camera's still on. Okay, so let's look at these equations quickly. I started hate doing this because it I'd rather you were paying attention and writing them down. So we've got methanol graphite age, too, and oh, to notice we have a couple fractions here that can happen. So in our first equation, Methanol plus Oxygen Yield Co two and H +20 and then graphite. That's what you're writing with. If you're using mechanical pencil or any kind of pencil, Um plus oxygen yields CO. Two hydrogen and oxygen unions, water and Here's our heat terms. Notice that they're all negative for three given equations. And here's what we want. This is important. We want graphite plus hydrogen plus oxygen yields. Method all we need to find the heat turn. Let's begin. So I'm going to write one to and three, and we're gonna put our equations in. Okay, I'm gonna start with the equation number two because graphite is on the react inside for my target. And it's on my react insight here, so I'm going to start with my graphite, plus my +02 yields CO two. And since I didn't do anything to this, I'm gonna leave my delta H as exactly 3 93 0.5. Kill a Jules per mole. Okay, one equation. Done. Now, I'm gonna look at equation too. I would like to get I think I'll switch colors for this for equation two. I want to get mine ethanol on the product side. So I'm going to flip if you will. This equation, these two products are now going to be my react. It's Let's write them down. C 02 g plus two h +20 And on my practice side, I'm going to have CHD o h plus 3/2 +02 and my delta h. I also have to flip my sign. So now this is going to be positive. 7 26.4 killer jewels per mole. And last but not least, we have our, um, water. And for this reaction, um, you'll notice I do not have water in this reaction. So the waters here have to cross out, which means I need to keep this seek water on this side. You could also look and see that I need Hydrogen is here. Doesn't really matter long as you get the right one. So my delta h for this will also be the same. It's negative to 85.8 and not a room. They're killing joules per mole, and I'm almost done. But I have one more thing I need to do here. Let's go to green now. I don't have a sufficient amount of water here, so I need to multiply this whole equation, including the heat term by two. So I need to multiply this by two two times negative to 85.8 and I will get end up with two hydrogen, one oxygen and two waters. And now I could cross out those terms that appear exactly the same on both sides of the arrows. So to waters and two waters. Goodbye. One carbon dioxide in one carbon dioxide. Goodbye. Now the oxygen's air. Little trickier. Please note that I have one plus one. I have to. Oxygen's right here, and I have 1.5 Oxygen's right here. So I'm left with an excess of 1/2 02 on this side of the equation. So I'm just gonna put a single line through all these because I took care of that. Now, my final equation. I've got this term. See, graphite, I have to hide regions, and I have half oven oxygen and that satisfies all three of these. And my only product is C H 30 H. Now, for the mathematical part of this, we're going to take positive. 7 26.4 These are all killer jewels. Plus killed Jules promote negative 3 93.5 plus two times negative to 85.8. Again. All killing joules per mole. And when I'm done here when we find my paper, I got negative. I'm going to switch colors. Negative to 38 point seven. Kila jewels, Perm all Let me write my answer Right here. Negative to 38 0.7. Kill a Jules per mole. These aren't hard, but just keep keep organized. I'd like to try to line my arrows up best I can.

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