Question

the first area is supposed to be kg km^2 year^-1

5. The photosynthesis of aquatic plants is given by the balanced chemical reaction 6CO2(g) + 6H2O → C6H12O6(s) + 6O2(g) leading to carbon fixation in the oceans. It is estimated that the mass of carbon fixed in the oceans is 44,5 x 10 kg km year. Calculate the annual enthalpy change of photosynthetic carbon fixation in the ocean per mole of carbon assuming 298 K and 1 atm. Oceans cover -71% of the Earth's surface which is about 3.6 x 108 km?

Answer 1

6 CO₂(g) + 6 H₂O(l) $\rightarrow$ C₆H₁₂O₆(s) + 6 O₂(g)

∆H = 6× 0 + 1×(-1260) - 6×(-285.83) - 6×(-393.51)

= 2816.04 kJ/mol

Area of ocean = 71/100 × 3.6×10⁸km² = 2.556×10⁸km²

Mass of carbon fixed per year by oceans = 44.5×10³kg/km².yr × 2.556×10⁸km² = 113.742×10¹¹ kg/yr

Number of moles of Carbon fixed per year = 113.742×10¹⁴g/year ÷ 12g/mol = 9.4785×10¹⁴mol/year

Number of moles of CO₂ fixed = 9.4785×10¹⁴mol/year

∆H = (2816.04/6)kJ/CO₂× 9.4785×10¹⁴ mol/year

= 4.449×10¹⁷ kJ/(mol C.year)

= 4.45×10¹⁷ kJ/ (mol C.year ). (Answer)