The equation for the combustion of propane and corresponding enthalpy of reaction is shown below. C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l) ...

Calculate the enthalpy change when $5.00 \mathrm{~g}$ of propane is burned with excess oxygen according to the reaction $$\mathrm{C}_{3} \mathrm{H}_{8}(g)+5 \mathrm{O}_{2}(g) \rightarrow 3 \mathrm{CO}_{2}(g)+4 \mathrm{H}_{2}\mathrm{O}(l) \quad \Delta H=-2221 \mathrm{~kJ} / \mathrm{mol}$$

Mhm. So Germany entropy of combustion for propane, propane as a chemical formula C three H eight. Gas phase combustion is plus oxygen gas Were produced co two gas. And to a gas to balance this, we need a five here, Three here and for here. So to determine the entropy of combustion here. Yeah. We're going to start with carbon solid or to gas. Pretty sick. Co two gas first about the age not Formation here is equal to -394 Villa jewels per mole. Then we'll have age too. Yes, Plus 102 gas. And this will produce H20. Gas lT it's not formation Is equal to -242. So the jewels per mole. And Then we have c. three J gas. Mhm. Mhm. Which will produce three carbon solid. Mhm. And for each to gas. And this has given to us the question As 104 kg per mole. Mhm. Well Let's multiply this by three, 3, 3 and three. We'll take this and multiply it by three. Take the second one will multiply it by four. So before for and four fiscal here we multiplied by four. If we combine all this together here, we'll see that the four H two S will counsel three carbons will cancel and we left today. C three H eight gas combined, the oxygen's at 502 Gas will produce three C 02 gas And four H 20 gas. And if we add up all of our up ph not values the the th the entropy of combustion here works out to minus 2000 and 46 killer jewels promote.

Okay. So this question actually testify your knowledge on how to use The entropy of other reactions right? To calculate one reactions. So the reaction you want we want to calculate right, is the combustion of the propane. So first let's write down the reaction, right? Which is? We had a C3ha propane and react with oxygen. Okay. Mhm. And we're full carbon dioxide, street carbon dioxide and for water. And in this problem we will actually want to calculate right. The standard uh entropy of the combustion and what it gives us is actually the formation energy of the water, carbon dioxide and the formation entropy of the propane. Right? So that's first right down this three formation entropy is right. So first we have the formation entropy of the water which equals two. You can check on the table. It's equal to minors. 285 points five. Killer Joke for More. And the reaction correspond to this S. O. P. Is actually you have the hydrogen right react With 1/2 water molecules forms water. So this is the reaction correspond to the formation entropy of the uh huh answer p of the formation the water. And the second uh number the question gives us is a formation entropy information of the carbon dioxide. And we can check from the table which equals 2 -393.5 p. A job for more. So we can write down its corresponding reactions which is carbon, right composts its oxygen and form carbon dioxide. And the 3rd information this question gives us is the formation energy of the propane which equals two miners one of four que no joke for more and same. We need to write down its corresponding reactions right? Which right we have It's pure substance, right? Carbon a solid and hydrogen has CASS and they react to form the propane. So we have to balance that with three carbons and four hydrogen molecules. So, through the observation, right, how can we uh, From this chemical formula? Right. With the former 1, 2, 3. You see this formula has one propane, right? And formed three carbon dioxide and for water. And for the first question that one hydrogen right from one water and one carbon from one carbon dioxide. So through observation, you're fine. Right for this reaction as we mentioned, was as a. That's right again, right for this reaction, which is what we want to calculate. Yeah, distraction. Right through action four. This one, right. It's actually equals two. You can see actually equals two. Four times Was the reaction one plus, right, three times the reaction to because there was three carbon dioxide form right through the combustion miners. One reactions three and this equals to write their reaction for and the same right? For the delta age of such reaction right? Actually equals to four times the answer. Key information the reaction warm. Which is the information. That was the water. Right? And applause Three times the entropy of the reaction to which is the formation entropy of formation of the carbon dioxide Miners. Right. Reaction three, which is the formation energy formation and the people of formation for the propane. And that's plugging the number. Right. Four times here it's right -285.5 plus three times miners. 393 0.5 miners. This right -104. And use your calculator. You'll find the entropy of this combustion Is -2260. Cute joe for more. It's a pretty large number and this is the answer. And this is kind of question which is very usually tested in the uh, in the exams. So you need to be careful on that and you should spend more time practicing this kind of solving these kind of questions.

So the equation for the combustion off JC's methanol is listed at two ch 30 H in the G A. C is one of three or two, and also in the gay c'est form, which generates to co two and full waters. So, using bond association and for peace here, we're estimating the answer would change for this reaction. So let's look at our calculations. So calculating from bond association and puppies are doubts are eight is negative. 1000 and 70 in Kelly Jones Pummel I doubt h is negative. 525 killer jewels from old for our methanol. Now we're calculating from our thermal chemical data. Where are doubts are h is negative. 1352 villages pummel in the reaction and are dealt H is negative. 676 Keller jewels, part mall. So our thermal chemical data values are ever so slightly lower, then our bond association and API approximations here. Andi, I say lower, even though the number is higher on the screen. But you do need to be wary off that negative charge. We start at zero, will increase up to 1000 and then we decrease down to 1000. So even if the numbers decreasing, we're just going farther and farther down.

So in order to get these three equations to add up to the main equation here, we'll need The Siege four on the left and we need two of them. So we need to times this equation And then the Delta H Times two and then we'll need C2 H six, only one of them um on the right hand side. So we're going to multiply, we're basically going to reverse the equation and multiply it by a half and then we're also going to need to do the same thing for the the only equation containing H two, we want one H two we wanted on the right sort of ours the equation and multiply it by so the overall delta H is going to be the sum of these new delta H values. So let's do it out. So we have 890.3 which is negative and times two is negative 17 80.6 four -5, times a half negative half. I mean there's going to be positive To 85.8 and then negative 31 20 .8 times negative a half Is 15 60.4. And so when we add them up we get a small positive number for the overall reaction. You should of course check to see that these three, when you manipulate them add up to the desired equation, it's impossible to make mistakes, but there we go and then we get 65.6 collaterals slightly and a thermic.