Question

Consider the formation of glucose from carbon dioxide and water (i.e., the reaction of the photosynthetic process): 6CO2(g)+6H2O(l)→C6H12O6(s)+6O2(g) .
The following table of information will be useful in working this problem:

T= 298 K	CO2(g)	H2O(l)	C6H12O6(s)	O2(g)
ΔH∘f (kJ mol−1)	-393.5	-285.8	-1273.1	0.0
S∘ (J mol−1 K−1)	213.8	70.0	209.2	205.2
C∘P,m (J mol−1 K−1)	37.1	75.3	219.2	29.4

Calculate the entropy change for this chemical system at T = 298 K.

Calculate the enthalpy change for this chemical system at T = 298

Calculate the entropy change of the surroundings at T = 298 K

Calculate the entropy change of the universe at T = 298 K

Calculate the entropy change for this chemical system at 320. K

Calculate the enthalpy change for this chemical system at 320. K

Calculate the entropy change of the surroundings at 320. K

Calculate the entropy change of the universe at 320. K

Answer 1

The given chemical equation is:

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

(a): At 298K, the entropy values are called standard entropies.

The formula for standard entropy change for a chemical reaction is:

S^o = (Standard entropies of all products) - (Standard entropies of all reactants)

=> S^o = [S^o(C6H12O6,s) + 6*S^o(O2,g)] - [6*S^o(CO2,g) + 6*S^o(H2O,l)]

=>  S^o = [209.2 + 6*205.2] - [6*213.8 + 6*70]

=> S^o = 1440.4 - 1702.8

=> S^o (sys) = - 262.4 J/K (answer)

(b): At 298K, the enthalpy of formation values are standard enthalpy of formation.

The formula for standard enthalpy change for a chemical reaction is:

H^o_rxn = (Standard enthalpy of formation of all products) - (Standard enthalpy of formation of all reactants)

=> H^o_rxn = [H^o_f(C6H12O6,s) + 6*H^o_f(O2,g)] - [6*H^o_f(CO2,g) + 6*H^o_f(H2O,l)]

=>  H^o_rxn = [- 1273.1 + 6*0] - [6*(-393.5) + 6*(-285.8)]

=> H^o_rxn  = (- 1273.1) - (- 4075.8)

=> H^o_rxn = 2802.7 KJ (answer)

(c):  S^o(surr) at 298K =  - (H^o_sys) / T = - (2802.7 KJ) / 298 K = - 9.405 kJ*K^-1 * (1000 K / 1 kJ)

= - 9405 J*K^-1 (answer)

(d): S^o(sys) + S^o (surr) = S^o (univ)

=>  S^o (univ) at 298K=  - 262.4 J/K- 9405 J*K^-1 = - 9667.4 J*K^-1 (answer)