Problem 148 Hard Difficulty

The heating value of combustible fuels is evaluated based on the quantities known as the higher heating value (HHV) and the lower heating value (LHV). The HHV has a higher absolute value and assumes that the water formed in the combustion reaction is formed in the liquid state. The LHV has a lower absolute value and assumes that the water formed in the combustion reaction is formed in the gaseous state. The LHV is therefore the sum of the HHV (which is negative) and the heat of vaporization of water for the number of moles of water formed in the reaction (which is positive). The table on the right lists the enthalpy of combustion-which is equivalent to the HHV-for several closely related hydrocarbons.
Use the information in the table at right to answer the following questions:
a. Write two balanced equations for the combustion of C3H8;= one equation assuming the formation of liquid water and the other equation assuming the formation of gaseous water.
b. Given that the heat of vaporization of water is 44.0 kJ/mol, what is Hrxn for each of the reactions in part a? Which quantity is the HHV? The LLV?
c. When propane is used to cook in an outdoor grill, is the amount of heat released the HHV or the LLV? What amount of heat is released upon combustion of 1.00 kg of propane in an outdoor grill?
d. For each CH2 unit added to a linear alkane, what is the average increase in the absolute value of Hcomb?

Answer

Answer not Available

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Video Transcript

so this problem starts. Bye. Ah, Writing the balanced equation for the combustion of propane to form liquid water and gashes water And so we'LL start with Ah, gashes Water. So see three h eight gas plus five oh two gas forms for H two o gas plus three CO to gas And then we'LL write the same thing again. But with the on ly change being liquid water, so then moving into problem B, we want to find the Delta h of reaction of each of these. And so since it gives the Delta H of combustion for this first reaction being the H H v ah, as negative two to one nine Killa Jules per mall. We know that's our answer. And as far as the Delta H reaction for the one with liquid water, we just take our two to one nine killer Jules per mall and add the heat of vaporization of water times the number of moles of water. And this is I explained in the problem. And that gives us an answer of negative to zero for three. Kill a Jules Permal. Now moving on to letter C. It asks when propane is burned on a propane fueled grill. Aah! What is the heat released is at the H H V or the elegy, and it is the H H V because we are creating Htoo gas when we do that. And then it asked us to determine the amount of heat released from one kilogram of propane. And so we start out with our two to one nine killer Jules per mole, we divide by the Moler massive propane, forty four point one grams per mole. And then we just convert grams two kilograms, and then we get our answer as fifty thousand three hundred seventeen killer jewels of energy are released from one kilogram of propane and now go to a new page for letter D. And this asks us what is the average increase in the absolute value? Ah, based on the table off these ah heats of combustion, when we add another carbon to the chain. And so we just take the higher value and subtract the lower value from the table. And we just do this for all the values all the way down the table. And then we can divide our final answer by seven. Since we will have seven of these, and that will give us the average. So all of these values are from the table. And I'm just going down and subtracting by the previous one, taking the absolute value of both and doing this on. Then we divide the whole thing by seven. And doing this gives us an average increase of six six, fifty four point three Killer Jules promote And that is our final answer for letter D.

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