Burning Calories

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Burning Calories

Postby amyc » Mon Jan 28, 2013 12:23 pm

Questions from student. Project due tomorrow:

Project: Burning Calories: How Much Energy is Stored in Different Types of Food?
http://www.sciencebuddies.org/science-f ... p012.shtml

I was burning a marshmallow and I did the math to figure out that 1 marshmallow should have 12.21 Calories (from the nutrition label) but the answer came out to be .2 Calories! I don’t understand what I did wrong. I repeatedly tried but it never came out right. When I burned the food and measured the initial temperature and final temperature of the water, the it came out to 200 calories, or .2 kilo calories.

I did it like so: Q=100g * 1 cal/g*C * (21 C-19 C) so Q=200 calories or .2 kCal

Does this Calorimeter actually measure the calories in food or does heat escape and mess up the answer? My question for my experiment is: How much energy is stored in different kinds of packaged food and how does this compare to its nutrition label? I am not sure if this experiment will work at all now since it does not give me numbers even close to the actual calorie amount.
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Re: Burning Calories

Postby donnahardy2 » Mon Jan 28, 2013 2:27 pm


Your experiment definitely worked because you have obtained some results so your project is a success.. If you did the experiment repeatedly, and obtained the same results, then you got the right answer. Getting reproducible results is always good with science projects.

Since you don't have time to continue the experiments, you should definitely continue writing up your display board and enter the project with your results as they are.

Here is the information on the display board from the Science Buddies website. Be sure and include all sections.

http://www.sciencebuddies.org/science-f ... oard.shtml

Since your results did not turn out to be as expected, your discussion and conclusion section will be more interesting compared to some of the other projects, You need to include a complete discussion and explain what happened. Here are my suggestions for this section:

1. First, let's check your calculations. First, can you confirm that you used 100 grams of water? If you did, then your calculations are correct; 100 grams of water multiplied by 2 degrees Centigrade for one marshmallow equals 200 calories of 0.2 kCal.

2. Possible sources of error.

First, you should calculate the percent error in your results. Percent error = 0.2 kCal minus 12.2 kCal divided by 12.2. kCal. Minus 98%.

So your calorimeter did not capture 98% of the expected energy from the burning marshmallow. Where did all of the heat go to? Perhaps one or more of the following contributed to the heat loss?

1. Did your marshmallow burn completely? It should have turned completely to ashes.
2. Was the burning marshmallow very close to the water? Some of the heat was transferred to air, rather than to the water.
3. How long was required to measure the heat produced by burning one marshmallow? The water would have been cooling during the experiment,
4. What was the accuracy of your thermometer? If it only measures whole numbers, then you might have missed up to a degree of temperature change.
5. Was there any disturbance in the air, such as a fan, that would have accelerated cooling during the experiments.
6. When you were taking the temperature of the water, did you mix the water to ensure that you were measure the average temperature of the entire water sample?
7. Why do you think that one marshmallow has 12.2 calories? Did you verify the accuracy of this information?


Use the answers to these questions and anything else you can think of to explain why your answer was so low. The science fair judges will be interested in knowing whether you understand the science behind your project and your ability to analyze results. That is actually more important compared to getting the right answer.

Next, write a paragraph explaining what you would do differently if you had time to repeat the results. How would you improve the design of the calorimeter? Would you change anything about the experimental design?

You have a complete science project and it will be a very good entry if you complete the write up and presentation.
Good luck!

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