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I performed an energy content experiment the other day using a rudimentary bomb calorimeter. The experiment was comparing for the energy release of a sugary food (Arnott's Tiny Teddies) to the energy release of a starchy food (Water Cracker).

It was observed that the starchy food was much easier to ignite and was kept alight for longer. The sugary food needed a lot more heat to ignite and didn't stay alight for as long.

In the results it was found that the starchy food released less energy per mass compared to the the sugary food.

Is there any obvious reason why the starchy and sugary foods burn this way and release these relative amounts of energy? I assume it may be due to the chain structure of amylose/amylopectin compared to the smaller structure of sucrose, but I'm not 100% sure.

Thanks!

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  • $\begingroup$ I assume the ignition heat value has been involved in the energy balance. $\endgroup$
    – Poutnik
    Sep 27, 2023 at 7:29
  • $\begingroup$ The samples were heated over a Bunsen burner to initiate the flame. This does result in an error of mass loss while the sample is not underneath the water (used to calculate the energy released). $\endgroup$
    – Thomas
    Sep 27, 2023 at 7:48
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    $\begingroup$ You should describe in the question all relevant details of the experiment. Otherwise it leads to guessing and possible misinterpretation. // Generally, the calorimetry does not care about combustion kinetics assuming the combustion is complete and all energy flows are considered. $\endgroup$
    – Poutnik
    Sep 27, 2023 at 7:52
  • $\begingroup$ You are looking at three different things, two somewhat related. One is the ease with which you ignite the substances, the second is how long they burn, the third is how much energy they release. That last question can be answered with fair precision if you know the weight and composition. $\endgroup$
    – Buck Thorn
    Sep 28, 2023 at 7:51

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Is there any obvious reason why the starchy and sugary foods burn this way and release these relative amounts of energy?

No, because the experiment did not test pure starch and pure sugar. The water content plays a role in flammability (does not burn, takes energy to get into the gas phase), and the fat content plays a role (burns very well, and is more exothermic per gram of fuel than carbs).

Here are two random food labels resembling your materials:

Honey tiny teddy: enter image description here

Some brand water cracker: enter image description here

Water content

For the cracker, the mass of carbohydrates, fats and proteins adds up to 29 g for the 30 g serving, so there is little water (it's a cracker).

For the cookies, non-water ingredients add up to 24 g for the 25 g serving, so also quite dry.

Fat content

The cookies have about 13% (by weight) fat, the crackers about 17%.

Starch vs. Sugar

You have to add water to starch to break it down to simple sugars. You could write a thermodynamic cycle to see how this influences the comparative energies of combustion (or enthalpies, if you are working with constant pressure).

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