Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest-burning octanes is a compound called $2,3,4-$ trimethylpentane, which has the following structural formula:

$$\begin{array}{c}{\mathrm{CH}_{3} \mathrm{CH}_{3} \mathrm{CH}_{3}} \\ {\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}-\mathrm{CH}-\mathrm{CH}-\mathrm{CH}_{3}}\end{array}$$

The complete combustion of one mole of this com-

pound to $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(g)$ leads to $\Delta H^{\circ}=-5064.9 \mathrm{kJ}$ (a) Write a balanced equation for the combustion of 1 mol of $\mathrm{C}_{8} \mathrm{H}_{18}(l) .$ (b) By using the information in this problem and data in Table $5.3,$ calculate $\Delta H_{f}^{\circ}$ for $2,3,4$ -trimethylpentane.

## Discussion

## Video Transcript

All right, guys say we're going to be he looking at problems. Problem number seventy four are we're going to be looking at figure out thie standard rental p of re of reaction for these four different reactions. So in first one, we have calcium oxide wreck of a child from katherine chloride and water. Remember that the age of reaction is equal to the delta h approx monthly a Delta H other reactions That's has his law. No. So we're going to do this. So minus two. Forty one point eight two two minus ninety two. Wait, three is your minus. That's it. That's right. As the wrong number minus seven. Ninety five point eight minus two times ninety two point three three minus six. Thirty five point five. And that is five. So that s O that Delta H for here is minus two seventeen, twenty five to still a jewels from all. Now, for this question, we're going to do that's us, remember And Molly, an element in standard state, like oh to, for example, the Delta zero. So we have eight. Twenty two as our only product to a twenty point sixteen minus four times minus two. Seventy one point nine. Fine. So are the H is going to be two. Sixty five point four for killing Jules Promote. It's again. We're going to do what we've been doing before. So s O and a two. Thirty three point eight four minus one. Seventy point seven minus the reactant. So ninety point three seven minus two times negative. One. Fifty six point one. You know why I don't care? Those ages five thirty nine point four three Kill a Jules. And now we're going to be going too. That's two. Number four or so we have. That's it. We are going to do the same thing you've been doing before for remember. Oh, too, there's no doubt H value for that. So two times at most. Two. Eighty five eight three plus ninety by point four zero minus snus. Four times they could have forty six point one nine. Fine. So we have to. That's like two eight eight three plus ninety five point for minus four time Negative. Forty six tonight, one nine. So that means our adult age value is two two, ninety one point five. Kill a Jules Ramon so we can use has his law to figure out the term of the enemy of every reaction. Just member Delta Age of your reaction is the The Delta H of the reaction is equal to us is equal to the price minus l th reactive. And it's I just one moment I want to make sure that I did not make a mistake here. And I believe I did this minus ninety three, seven minutes to us, too. Yeah, that they mistake big. This should be a plus sign. I think the actual answer is eighty four point nine seven. I apologize for the inconvenience.

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