Question

You are working in an alternative fuels laboratory and have been asked by your supervisor to determine the efficiency of photosynthesis for a plant that is being considered as a source of biofuels. You know that the plant produces the equivalent of 24 kg of sucrose per hectare per hour. You also know that sun supplies energy at a rate of 1.0 kilowatt per square meter of surface area. Assume that sucrose is produced by the reaction: 12 CO3 (g) + 11 H2O (g) ? C12H22O11 (s) + 12O2 (l) ? H = -5640 kJ

Answer 1

Moles of sucrose = mass of sucrose/molecular weight

= (24kg x 1000g/kg) / (342.3 g/mol)

= [70.114 mol/(hr-ha)] x (1ha/10000m2) x (1hr/3600s)

= 1.948 x 10^-6 mol/(m2-s)

Energy required for photosynthesis = 5640 kJ/mol

Energy needed to produce 24 kg sucrose

= Energy required for photosynthesis x Moles of sucrose

= (5640 kJ/mol) x [1.948 x 10^-6 mol/(m2-s)]

= 0.01098 kJ/(m2-s)

Energy supplied from sun = 1 kW/m2 = 1kJ/(m2-s)

Efficiency for photosynthesis

= (Energy needed to produce 24 kg sucrose) / (Energy supplied from sun)

= [0.01098 kJ/(m2-s)] / [1kJ/(m2-s)]

= 0.01098 x 100

= 1.098 %