Without doing the actual calculation, estimate the fuel...

Name: Problem 50, Chapter 20: Chemistry The Science in Context
Uploaded: 2020-05-14T23:18:55-08:00
Duration: 4 min 39 s
Channel: Charles Thomas
Description: Without doing the actual calculation, estimate the fuel values of glucose and starch by considering average bond energies. Do you predict the fuel values of the two substances to be the same or different?

Without doing the actual calculation, estimate the fuel values of glucose and starch by considering average bond energies. Do you predict the fuel values of the two substances to be the same or different?

Key Concepts

Molecular Structure and Polymerization

The molecular structure of a compound, including whether it is a monomer or a polymer, plays a crucial role in its overall energy content. For carbohydrates, a monosaccharide and its polymeric form (linked by glycosidic bonds) will have similar energy contents per repeating unit. However, the energy required to form or break the bonds linking these units (as in polymerization) can lead to slight differences in the overall fuel value when comparing the substances on a per mole or per gram basis.

Fuel Value Estimation

The fuel value of a substance is determined by the energy released during its combustion, which can be approximated by summing the energies of the bonds broken and formed during the reaction. By using average bond energies, one can make rough predictions about the total energy output of a reaction without detailed calculations, providing insight into the efficiency and performance of different fuels.

Bond Energies

Bond energies refer to the average amount of energy needed to break a chemical bond in a molecule. In thermochemistry, these values allow us to estimate the energy changes during chemical reactions, such as combustion, by comparing the total energy required to break bonds in reactants with the energy released when new bonds form in the products.

Transcript

00:01 So this question is about whether the fuel values of starch, which is a polymer of glucose and glucose.

00:11 And it first asks us to estimate the fuel values without doing the calculation, which we really cannot do.

00:19 I think what it's really asking us to do is to compare the fuel values for the two and to predict whether they will be the same fuel value, or different.

00:33 First of all, in the, so maltose is just a disaccharide, but it does illustrate the alpha -14 linkage.

00:43 So this is the number one carbon on that glucose unit, and this is the number four carbon on this glucose unit.

00:51 And so in forming that glycosidic alpha -1 -4 linkage, there is an h -2 -o molecule loss.

01:00 So if you consider the oh group on one glucose molecule at the number one position and on another glucose molecule at the number four position, between the two of them, they've got two hs and two o's.

01:19 But then in the polymer with the linkage like we have here in maltos, you just have one o.

01:26 So there's loss of a water molecule.

01:31 And so on a per gram basis, that gives the starch an advantage because it has a mass that's 5 % less per glucose unit than glucose itself does.

01:48 That one water molecule is 5 % of the weight of each dimer.

01:55 But ignoring that, what really is the difference between the use of glucose as a fuel and the use of just a dimer unit as fuel? that would be, let me see...

Please give Ace some feedback