Ethanol is a possible fuel. Use average bond energies to calculate ΔHrxn for the combustion of ethanol. CH3CH2OH( g) + 3 O2( g)¡2 CO2( g) + 3 H2O( g)

Video transcript

Welcome back everyone to another video bean 10 is a possible fuel use average bond energies to calculate the entropy change of the reaction for the combustion of U 1010 We're given the reaction C 4h 90 liquid reacts with six moles of 02 gas and they produce four moles of CO2 gas and five moles of h2o gas. We're given for enter choices a 1.23 multiplied by its sense of the third kilojoules. B negative 2.45 multiplied by its sense of the third kilojoules. C 1.96 multiplied by its sense of the fourth kilojoules in the negative 9.81 multiplied by its sense of the third kilojoules. Let's solve this problem. And because we're using the average bond energies where we essentially need to understand the structure of each compound. The first one is an alcohol. So what we want to do is just to draw our four membered carbon chain, we're going to add our alcohol group to the very first carbon because it says B 1010, we can actually add it at the end because that can also be our carbon number one. And now we want to add the remaining nine hydrogens, every carbon must have more bonds. We can just add those bonds 123456789. And we can simply add those remaining hydrogens. The reason why we're doing this is simply because we want to understand what type of bonds we have or I'll react in some products. We're adding six moles of oxygen gas. We know that oxygen forms a double bond. And now we are forming four moles of Co2 co2 has two carbon oxygen, double bonds plus five moles of h2o hoh. Right? So now what we need to think about is the entropy of the bonds broken, the total entropy change of the bonds broken. We can start with calculating the entropy change of the bonds broken, let's call it BB. OK. And now we want to understand what type of bonds we have. Well, essentially we have a lot of carbon hydrant bonds. We have 123456789, right? So what we're going to say is that we're taking nine moles multiplied by the bond energy of the CH bond. OK. And for that purpose, we need to use our tables. We notice that the bond energy of CH would be 414 kilojoules per mole. We now need to add the CC bo entropies, right? Specifically, we have 123 CC bonds, we are taking three moles and multiplying by the CC bond entropy, that'd be 347 kilojoules per mile. What else do we have? Well, essentially we have our CEO bond, we have one mole, right? So we are going to say one mole multiplied by. Now, the co bond entropy would be 360 kilojoules per mile. We also have a 10 mole. So we are going to say one mole multiplied by the oh bond entropy which would be 464. I ju eventually, we have six moles of oo double bonds. So we're saying plus six moles multiplied by the bond entropy. If we look at the tables, we have 400 and 98 kilojoules per month. Let's perform the calculations. We end up with 8579 kilojoules. Our next step is to calculate the entropy change of the bonds formed. Let's call it BF. Now, for this one, we first will notice that we have four moles multiplied by two because we have two co double bonds. So a total of eight moles of co double bonds. The bond entropy for the co double bond would be 799 kilojoules per mole. And now, similarly, we're adding five moles multiplied by two multiplied by the bond entropy of the O bond, which is 464 kilojoules per mole. So once again, we have five moles of H two molecules, each molecule has two moles of our wage bonds. That's why we are multiplying by two. And if we calculate the result, we get 1 11,032 killer shaws. And now let's simply recall that the entropy change of the reaction is simply the difference between the entropy change of the bonds broken and the entropy change of the bonds formed. So we are essentially saying that in this case, we are subtracting 8000 500 and 79 killer tools and 11,032 kilojoules, which gives us our final answer negative 2400 and 50 kilojoules. In a scientific notation, we can clearly see that this corresponds to the answer choice and B that would be it for today. And thank you for watching.