6. Combustion! In this problem you will test the idea that most of the calories

Question

6. Combustion! In this problem you will test the idea that most of the calories in food product come from fats, carbohydrates, and protein. Find out how many grams of fats/carbohydrates/protein are in the following food products (see the "nutritional information" panel on the product container or look up the info online) per gram. Then use the following approximate enthalpies of combustion for fat", "carbohydrate", and "protein (-39 kJ/g, -16.5 kJ/g, and -23 kJ/g, respectively) to estimate what the caloric content would be for each food product. Compare the value you calculate for calories with the value provided by the manufacturer. Recall that nutritional calories, or kcal, are 1000 scientific calories, and that there are 4.18 Joules in one scientific calorie.

Explanation / Answer

In this question you are asked to calculate the caloric value of a food using heat of combustion values yourself and then compare it to the value which has been provided on the label by the food product manufacturer.

Let's say for a particular food item you choose, the fat content is listed as 'x' gm, protein content is listed as 'y' gm and carbohydrate content is listed as 'z' gm

Generally these values are listed as % values of the total product weight, so be sure make the conversion into absolute values.

Next, use the enthalpy values to determine the total heat content of the food product.

Heat produced by combustion of fat content = 39*x kJ

Heat produced by combustion of protein content = 23*y kJ

Heat produced by combustion of carbohydrate content = 16.5*z kJ

Total heat produced = (39*x + 23*y + 16.5*z) kJ

Now, 1 kJ = 0.239 kcal (scientific)

Thus heat content in calories = [ (39*x + 23*y + 16.5*z) * 0.239 ] kcal (scientific) = [ (39*x + 23*y + 16.5*z) * 0.239 ] cal (nutritional)

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