Fuel Value Of A Substance
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Fuel Value Of A Substance

(a) Define the term fuel value.
(b) Carbohydrates, proteins and fats are foods with fuel values. So, they are sources of energy.
Which is a greater source of energy as food, 5 g of fat or 9 g of carbohydrate.
(c) A serving of a certain food contains 7 g fat, 9 g carbohydrate, and 1 g protein. Estimate the number of Calories in a serving of this food.
(d) The heat of combustion of fructose, c6H12O6, is -2812 kJ/mol. If a delicious apple weighing 120 g contains 16 g of fructose, what caloric content does the fructose contribute to the apple?

The strings: S7P6A66 (grouping/interaction - chemical).

The math:
Pj Problem of Interest is of type grouping/interaction (chemical).

(a): the fuel value of a substance is the amount of energy (usually heat) released when 1 g of the substance is combusted.

(b): the fuel values of:
Carbohydrate = 17 kJ/g
Protein = 17 kJ/g
Fat = 38 kJ/g

So, fuel value of 5 g of fat = 5 x 38 = 190 kJ
So, fuel value of 9 g of carbohydrate = 9 x 17 = 153 kJ
So, 5 g of fat is a greater energy source than 9 gram of carbohydrate.

(c): fuel values of:
7 g of fat = 7 x 38 = 266 kJ
9 g of carbohydrate = 9 x 17 = 153 kJ
1 g of protein = 1 x 17 = 17 kJ
So, total fuel value in a serving = 266 + 153 + 17 = 436 kJ
1 calorie = 4.184 J
So, 436 kJ = (436 x 103)/4.184 = 104 kilocalories
1 kilocalorie (kcal) = 1 Calories (Cal)
So, 104 kcal = 104 Cal.
So, the number of Calories in a serving = 104 Cal.

(d) Molar mass of c6H12O6 = 12x6 + 1x12 + 16x6 = 72 + 12 + 96 = 180 kg
So, heat of combustion/g = -2812/180 = -15.62 kJ/g
So, 16 g of c6H12O6 = 16 x -15.62 = -249.92 kJ . Negative sign indicates heat is released.
249.92 kJ = 249.92/4.184 kcalories = 59.73 kcal = 59.73 Calories.
So, the fructose in the apple contributes 59.73 Calories to the apple.

Math

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