2.30 Suppose that the radius of a typical cell is 10 mm and that inside it 106 ATP molecules are hydrolyzed each second. What is the power density of the cell in watts per cubic meter (1 W = 1 J s−1)? A computer battery delivers about 15 W and has a volume of 100 cm3. Which has the greater power density, the cell or the battery?

Respuesta :

Answer and Explanation: One ATP release approximately 30.5kJ/mol of energy. Using Avogadro's constant, it is known one mol corresponds to [tex]6.02.10^{23}[/tex] molecules, so 106 ATP molecules releases:

E = [tex]30.5.10^{3}*\frac{106}{6.02.10^{23}}[/tex]

E = [tex]537.04.10^{-20}[/tex]J

A cell is approximately a sphere. Volume of a sphere is given by

V = [tex]\frac{4}{3}.\pi.r^{3}[/tex]

Changing radius from mm to m:

r = [tex]10^{-2}[/tex]m

Then, volume is

V = [tex]\frac{4}{3}.\pi.(10^{-2})^{3}[/tex]

V = [tex]4.2.10^{-6}[/tex] m³

Power density is given by

[tex]power=\frac{energy}{volume}[/tex]

[tex]power=\frac{537.04.10^{-20}}{4.2.10^{-6}}[/tex]

[tex]power=128.10^{-14}[/tex]

power = 12.8.[tex]10^{-15}[/tex] W/m³

Power density for a the cell is 12.8.[tex]10^{-15}[/tex] W/m³.

Power density for battery is

100 cm³ = [tex]10^{-4}[/tex]m³

power = [tex]\frac{15}{10^{-4}}[/tex]

power = [tex]15.10^{4}[/tex]W/m³

Comparing cell and battery, battery has a greater power density.