Which is the least expensive source of enery in kilojoules per dollar, a box of breakfast cereal that weighs 32 ounces and costs $4.23, or a liter of isooctane (Density 0.6916 g/mL) that costs $0.45? Compare the nutritionl value of the cereal with the heat produced by combustion of the isooctane under standard conditions. A 1.0 -ounce serving of the cereal provides 130 calories

Respuesta :

Explanation:

1) 1.0 ounce serving of the cereal provides 130 calories.

Then 32 ounces of breakfast cereal will provide :

= [tex]32\times 130 cal =4160 cal[/tex]

Cost of 32 ounces of cereal = $4.23

Energy from cereal with respect to dollar:

[tex]\frac{4160 cal}{\$4.23}=983.45 cal/\$[/tex]

2) Density of iso-octane = d = 0.6916 g/mL

Mass of the iso-octane = m

Volume of iso-octane = V = 1 L

[tex]m=d\times V=0.6916 g/mL\times 1L = 0.6916 g[/tex]

Moles of isooctane = [tex]\frac{0.6916 g}{114 g/mol}=0.006066 mol[/tex]

Heat of combustion of isooctane = 5450 kJ/mol

Heat released on combustion of 0.006066 moles of isooctane:

[tex]0.006066 mol\times 5450 kJ/mol=33.0633 kJ[/tex]

1 kJ = 239.006 cal

[tex]33.0633 kJ=33.0633\times 239.006 cal=7,904.23 cal[/tex]

Cost of 0.6916 g or 1 L of isooctane = $0.45

Energy from isooctane with respect to dollar:

[tex]\frac{7,904.23 cal}{\$0.45}=17,564.95 cal/\$[/tex]

We can generate large amount of energy by combustion of isooctane than the energy we getting from cereal:

17,564.95 cal/$ > 983.45 cal/$

But isooctane is an indigestible by human body so, it will be good to have cereals.