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Problem 68

(a) What is the value of the standard enthalpy of formation of an element in its most stable form? (b) Write the chemical equation for the reaction whose enthalpy change is the standard enthalpy of formation of sucrose (table sugar), $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(s), \Delta H_{f}^{\circ}\left[\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(s)\right]$

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## Video Transcript

all right. Hey, guys, we're going to be doing problem number sixty eight in Chapter five of Chemistry Central Science. So this two part question party they wantto was the value. Have the Sandra and Toby permission for an element, its most stable form. The answer to that is zero the Delta H information of any element in its standard state state. It at center conditions is always going to be Go on, be zero. So oxygen is not found This mon atomic its founders O dia Tamiko, too. So it's always going to Delta H zero. Similarly, you need Delta age for age for F two, which is Florian's in its natural state is going to be zero Europe similarly, And put this as you can find that h information for H two o I to be our two. Those are also zero as well, so perfect. They want to write the chemical equation for the reaction. Who's entropy? Changes standard on the information of super Hans. Oh, so the way to solve this is to first, we're going to put our Super song the right. It's C twelve h twenty to eleven. No, and and Radium was selling Suker's here. So beast in the equation for the reaction who's dealt H is the standard Antal Pete information of sucrose That's actually going to be B the individual elements in their standard states coming together to form because, remember, has his law Delta H reaction equal to Delta H products as minus Delta? Each reactant. So if we're so our product is going, don't age approximately two Delta H information of our super's here, here, Delta h of reactant that's going to some of the Delta H values for elements. Understand? See and remember the Delta H for elements in their standard state that is going to be zero. So this so Delta H R. Is going to be easier. So that means that Delta h of reaction for shit For this for this chemical equation, he's going to equal the Delta h of our products, which is going to be equal to Delta H information of our super's. So let's get started. So we have twelve car bins on the on the right, so we have to have twelve on the left, left, left. Now we're gonna add our hydrogen and our O two. So now we have twenty two Hydra and left, left and right, trying to on the right toe too and left. So we're goingto put at eleven right here eleven times. Do there's going trying to in total. Now we have oxygen eleven option on the right and turn left. So we're gonna put the fraction eleven over two because eleven over to that is going to equal as as eleven over two is going to equal times two is going to equal eleven now. Needless to say, you cannot have half. A molecule is just a wage. Two. We can understand this kind of kind of reaction because the delta h of formation here us for supers. Is there any sample in general that only works if you're producing one mole of your sample? If you're not not, then you're going to have the wrong down to H age information. So that's why we have to have eleven eleven over to who tio two molecules is not that that we have half a molecule is just more of a visual represent of mathematical representation to understand and how we can have how we can have us finally does age us of one mole of supers, and that's how you solve the space. This basic setup, Remember, just to recap the Delta H formation of elements and most able form that is always zero. And when we want to find the Delta H information of a specific sample, the chemical questioning amusing is element in their standard state coming together to form one mole of our product.