Question

a.A peanut consists of 49.2% oil and 20.8% carbohydrate. (The remaining mass of the peanut is not combustible.) An average peanut has a mass of 0.75 grams. Determine the mass of oil and carbohydrate in one peanut. Then determine the amount of energy released (in kJ) when one peanut is burned

a.How many peanuts will it take to boil 1.00 liters of water?

Answer 1

Answer a. A peanut consists of 49.2% oil and 20.8% carbohydrate and the remaining mass of the peanut is not combustible. An average peanut has a mass of 0.75 grams. As we have to determine the mass of oil and carbohydrate in one peanut. So now we start calculation of oil and carbohydrate mass determination in one peanut weighing  0.75 g.

Mas of oil in one peanut = Percentage of oil in one peanut x Mass of one peanut = 49.2/100 x 0.75 g = 0.369 g

Mas of carbohydrate in one peanut = Percentage of carbohydrate in one peanut x Mass of one peanut =

20.8/100 x 0.75 g = 0.156 g

now we have to calculate amount of energy released in (kJ) when one peanut is burned =

Amount of energy released by burning 1 g of carbohydrate = 17 kJ/g

So amount of energy released by burning 0.156 g of carbohydrate found in one peanut = 17 kJ x 0.156 g= 2.652 kJ (a)

Amount of energy released by burning 1 g of oil = 37 kJ/g

So amount of energy released by burning 0.369 g of carbohydrate found in one peanut = 37 kJ x 0.369 g= 13.653 kJ (b)

So total amount of energy released by burning of one peanut = a + b = 2.652 + 13.653 = 16.305 kJ

Thus the amount of energy released (in kJ) when one peanut is burned is 16.305 kJ

Answer b . The y number of  peanuts is required to boil 1.00 liters of water. So now we solve for the value of y =

Amount of energy required to boil 1.00 liters of water is 2257 kJ/kg (value is known by standard values).

So number of peanut required to boil 1.00 liters of water (y) =

Amount of energy required to boil 1.00 liter of water/ Amount of energy released from one peanut =

2257 kJ/ 16.305 kJ = 138.42 peanut = 139 peanut

Thus answer is 139 peanut is required to to boil 1.00 liters of water.