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: The complete combustion of one mole of this compound to CO₂(g) and H₂O(g) leads to ΔH° = -5064.9 kJ. (b) By using the information in this problem and data in Table 5.3, calculate H°f for 2,3,4-trimethylpentane.

Video transcript

Hello. Everyone in this video, we're trying to calculate the standard entropy of formation for beautiful. So C. Four H. 90. H. And it's given that the complete combustion of one mole of vinyl releases this much heat. Alright, so we have a equation to use for calculating the standard and Topia formation and that's going to be let's spread this in black. So the delta H of a reaction is going to equal to the delta H. Affirmation of the products minus the delta age formation of erect. It's alright so here are some of the values that I'm going to be using to do this here. These products can also be provided to you by your professor or even given to you in your textbook. So I'll have that the delta H formation For c. 0. 2. Guess It's going to equal to negative 393.5 kila jules per Permal. And then my delta age information For my H 20 liquid. It's going to equal to negative 285. killer jewels, more lassie, my delta H affirmation of 02. It is going to be gas Is going to equal to zero. And let's not forget we also have this value right here. Alright, so now using this equation right over here we can continue and do our plug in the values to find the standard entropy of formation. And so let's do this in purple. So my delta age of reaction is given to us. Right so again, I'm just going to go ahead and rewrite this equation and so will have The value given to us in the problem as 0.45 killer jewels. And because we're if we go back to the problem just a little bit, it's saying that we're releasing this amount of heat when we're releasing this amount of heat that's going to be a negative charge or a negative sign. And so continuing on now, we have the delta age for our products. If you go back to the equation, the products, we have four moles of C. 02 and five moles of H 20. So we'll start off with the c. 0. 2. And so we have this value over here. So you have negative 393.5. And we're going to multiply this by four because we have four moles of the C. 02. And then we're gonna add this by the delta H. S. Of our H. 20. Which we have right over here. So we have negative 285. Times five for the five moles of H. 20. And then we're gonna go ahead and subtract this by all the delta H. Of formation of the reactors. And so we don't know what the delta age information for our C. four h. 90. H. But we do have the delta age affirmation for the 02. So put the delta H information for the C. Four H. 90. H. As an X. And then we'll have that to be multiplying. But it's pretty dark. So it gets this confusing times one And then we're adding zero. And this one right here is just because we have one more and then zero because six moles times zero is just zero. Now putting all this into my calculator to solve for my ex, we'll get that the X. Is going to equal to - 0.3 killer jules Permal. And again, just to replace the X. We said that the X. Is going to equal to the delta H. Of formation of our c. four age nine O. H. Compound. And it's again equal to negative 327.3 killer jewels Permal. And this is going to be my final answer for this question.