Lab 17: Calories in Food

Summary: In this lab, we burned three different types of foods: cheese puffs, brazil nuts, and cashew. The purpose of this was to find the number of the Calories per gram of different food items. We did this by lighting the snack on fire, placing a soup can calorimeter over the piece, and then placing a flask of water on top of the can. The calorimeter would keep the heat of the burning food contained, and the water in the flask above would absorb the heat. We kept track of how much its temperature increased from the absorbed heat using a thermometer. Afterwards, we calculated the amount of energy in the food by measuring the heat absorbed by the water, which was equal to the heat lost by the food.

Data:

Food	Initial Mass of Food (g)	Final Mass of Food (g)	Mass of Water (g)	Tinitial (°C)	Tfinal (°C)
Cheese Puff	0.960	0.150	25.0	22.1	42.3
Brazil Nut	3.86	1.70	25.0	24.4	60.2
Cashew	1.47	0.130	25.0	28.9	60.3

Food	Mass of food burned (g)	Change in Temperature (°C)	Q (calories)	Q (Calories)	Q / Mass of food burned (Cal/g)
Cheese Puff	0.810	20.2	505	0.505	.623
Brazil Nut	2.16	35.8	895	0.895	0.414
Cashew	1.34	31.4	785	0.785	0.506

Questions:

1. Did you measure a temperature change in the food sample or the water?

The food sample was impossible to measure; even if we had tried it most likely would have been inaccurate as it may have been exposed to the room temperature. In general, it would have been very hard to "submerge" the thermometer in the solid. We instead measured the temperature change in the water by placing a soup can calorimeter over the burning food and placing a flask of 25 mL water on top of it in order to indirectly heat the water. We placed a thermometer inside the beaker as well to let us track the starting and final temperatures.

2. Did you measure the energy released by the food sample or the energy gained by the water?

We measured the energy gained by the water, as it was easier to track than the energy the food sample released. As heat is related to energy, and temperature is related to heat, the fact that measuring the temperature of the water was done much more easily than had we tried to measure the food sample's temperature shows that measuring the energy released by the food sample would've been just as hard.

3. What happens to the small amount of energy that is not absorbed by the water?

We did the lab based on the assumption that "all energy was absorbed into the water," even though it was obviously not possible. The small amount was negligible, however, which is why the assumption was made. As energy cannot be destroyed, the small amount of energy not absorbed by the water was instead released into the air. 

4. Were you surprised by any of the results? Explain.

I was surprised the nuts had more calories than the cheese puffs; nuts have always seemed to be more "healthy" than snacks such as cheese puffs, but the latter had more than 200 less calories than either the cashew or the brazil nut.