Question

The net change in the multistep biochemical process of photosynthesis is that CO2 and H2O form glucose (C6H12O6) and O2. Chlorophyll absorbs light in the 600 to 700 nm region, (a) Write a balanced thermochemical equation for formation of 1.00 mol of glucose, (b) What is the minimum number of photons with λ = 680. nm needed to prepare 1.00 mol of glucose?

Answer 1

Sol.

(a) Balanced Equation :

6CO2(g) + 6H2O(l) -----> C6H12O6(s) + 6O2(g)   

(b) As Wavelength =   = 680 nm = 680 × 10^-9   m

So , Energy of one photon = E1 = hc /   

where h = Planck's constant = 6.626 × 10^-34 J s

c = Speed of light = 3 × 10⁸ m / s

So , E1 = 6.626 × 10^-34   × 3 × 10⁸ / ( 680 × 10^-9 )

= 0.02923    × 10^-17 J

Also , Standard Enthalpy change of balanced reaction = deltaH° = 2803 KJ = 2803 × 10³ J  

So , Energy of all photons = E = 2803 × 10³ J  

Therefore , Minimum number of photons needed to prepare 1 mol of glucose

= E / E1

= 2803 × 10³ / ( 0.02923 × 10^-17 )

= 95.8946 × 10²³