Question

Self-test 4.9 A hard-working human brain, perhaps one that is grappling with physical chemistry, operates at about 25 W (1 W = 1J s-'). What mass of glucose must be consumed to sustain that power output for an hour? Answer: 5.7 g sugars and persal of m released u are oxidize of organiz biological

Answer 1

Reaction in which glucose gets consumed to produce energy is as shown

+energy

C6H1206 +602(9) 6C02(g) + 6H2O(1)

Enthalpy for this reaction

=Sum of enthalpies of formation of products-sum of enthalpies of formation of reactants=

6ΔΗ,(co,9)) + 6ΔΗ, (H2O(1)) – 6ΔΗ,(Ο,g)) – ΔΗ(C6H2O5)

=6x-393.5 kJ/mol+6x-285.8 kJ/mol-6x0-(-1273.3 kJ/mol)

=-2361 kJ/mol- 1714.8 kJ/mol-0+1273.3 kJ/mol=-2802.5 kJ/mol x 1000 J/kJ (1 kJ=1000 J)

=2802500 J/mol

Power at which brain works=25 W

Energy required in 1 hour=Power x time

=25 W x 1 h

=25 W x 1 h x 60 min/h x 60 sec/min=90000 J

Number of moles of glucose used in 1 hour

=Energy required by brain in 1 hour/energy consumed per mole of glucose used

=90000 J/2802500 J/mol=0.032 mol

Molar mass of glucose (C₆H₁₂O₆)=6xMolar mass of C+12 x Molar mass of H+6 x Molar mass of O

=6x12 g/mol+12 x 1 g/mol+ 6 x 16 g/mol

=72 g/mol+12 g/mol+96 g/mol=180 g/mol

Mass of glucose consumed to sustain the power output for one hour=number of moles x molar mass

=0.032 mol x 180 g/mol=5.76 g