Science Buddies: "Ask an Expert"

I was planning on completing the Burning Calories: How Much Energy Is Stored In Different Types of Food? experiment for my science fair project this year. A large part of the science fair project is a review of literature on the background of our experiment. Instead of doing a variety of types of food for the experiment, I was only going to measure the amount of energy found in different types of nuts. The nuts I will be using are: pecans, almonds, and chestnuts. The problem is, I'm not really sure what to write my research paper about. My teacher said I could maybe find what's being burnt in the nuts, but I'm not sure what that is or how I could figure that out. Do you have any ideas? If not, is there anyone that has written a research paper similar to this one?

Hi,

Understanding the different types of nutrients in foods is very interesting and useful. Nuts are delicious and I tend to eat too many of them! If you look up the nutrients in a nut such as almond you will see that they contain fat, carbohydrates and protein and all of these can be used by the body to produce energy (http://nutritiondata.self.com/facts/nut ... cts/3085/2). Fats and carbs are used first as energy sources. Fats provide 9 calories per gram and carbohydrates, 4 calories per gram. Proteins are normally used as a source of amino acids for the body to rebuild its own proteins, and not as an energy source.

Some nuts such as walnuts contain high amounts of omega 3 fatty acids that are good for the blood system (http://www.livestrong.com/article/34459 ... tty-acids/). Seeds such as flax seed are also good sources of omega 3 fats. Nuts and seeds are not just good sources of energy. They have lots of other beneficial components such as fiber and the essential fatty acids (https://en.wikipedia.org/wiki/Essential_fatty_acid).

I prefer raw nuts and there is some evidence that roasting does alter the nutritional value slightly (http://www.prevention.com/content/which ... asted-nuts). You could include this in your report. There is also the hotly debated question about whether organic nuts and seeds are better for you than those from plants sprayed with pesticides (http://www.worldwellnesseducation.org/nuts-and-seeds/). This is another subject area that you could discuss in your report.

I hope this helps. If you have more questions please post again.

Sybee

I just completed the experiment and I have all of my data, but as I tried to calculate the Qwater I was really confused how to do it! I understand that I need the difference in water temperature, but I have no clue what the specific heat capacity of the water is or how to find it. I also measured my water in liters, not grams. Also, what does the difference in weight have to do with anything? Is it necessary? Thanks again!

Hi Mary,

The amount of energy absorbed by the water in your calorimeter, Qwater, is given by the equation in the procedure section: https://www.sciencebuddies.org/science- ... #procedure

The specific heat capacity, c is also given there and it is the amount of heat it takes to raise the temperature of 1 gram of water 1 degree C. By definition it is 1 calorie (abbreviated 'cal' with a lower-case 'c') per g . degree C.

However, the calories (abbreviated 'Cal' with upper-case 'C') that we talk about in food are actually equal to 1000 cal. The values you get from using the equation will be in cal so to convert them to Cal you have to divide by 1000 so your answers will be in Cal (also called 'kcal' or kilocalories) http://www.uta.edu/faculty/sawasthi/Lec ... alorie.htm

The mass of 1 liter of water is very close to 1000 grams. The mass varies slightly with temperature but since you are not using a real calorimeter you can assume the mass is constant at 1000 g.

Do the conversion to Cal/g as suggested in the instructions so you will be able to make a direct comparison of heat content among the different nuts.

Does this answer your questions ok? If not post again and we will try to help. Let us know your results. Did you see different Cal values for different nuts?

Good luck!

Sybee

Ok thanks again! So am I just supposed to divide the difference in water temperature by 1,000? Also, what is the equation used to find? Is it the amount of calories?

The Qwater that you calculate in the experiment is the energy in Cal that the water absorbed as a result of burning the food. The specific heat term in the equation, c, is the amount of energy required to raise the temp of 1 gram of water 1 deg C and is defined as one calorie (lower-case 'c' - cal). The energy of food is always given in kilocalories (1000 cal) and this is abbreviated as Cal or sometimes as kcal.

Since you used 1000 g (one liter) of water, this term will cancel out when you divided by 1000, so all you have to do is subtract the initial temp (in degrees C) from the final temp to get your answer in Cal.

For example, if the Ti = 20 C and the Tf = 35 C, then the food yielded 15 Cal upon combustion.

As I suggested before, you need to weigh the food before and after burning so you can convert your energy yield to Cal per g. All you have to do is subtract the weight in grams after burning from the initial weight to get the amount consumed, then divide this into the Cal value to get Cal per gram (Cal/g). By doing this, you will be able to directly compare each food.

Let us know if you have more questions.

Sybee