The total surface area of the earth consisting of forest, cultivated land, grassland, and desert is 1.49 x 1068 km^2.

The total surface area of the earth consisting of forest, cultivated land, grassland, and desert is 1.49 x 1068 km^2. Every year, the mass of carbon fixed by photosynthesis by vegetation covering this land surface according to the reaction 6CO2(g) + 6H20(l) --> C6H12O6(s) + 6O2 (g) is about 450. metric Tons km^(-2). Calculate the annual enthalpy change resulting from photosynthetic carbon fixation over the land surface given above. Assume P = 1 bar and T = 298 K.