Question

Calculate the standard free energy for the reaction given 1. 2 CH3OH(D +3 02(g) 2 CO2(g) 4 H20(0 AG fkJ/mol -166.4 0.0 Species 02 (8) CO2()344 H20 (2) -237.2 -797.8 kJ -2069.8 kJ 465.2 kJ -1404.8 kJ 2. At high temperatures boron carbide vaporizes according to the equation B4C(s)4 B(g) C(s) Which equation describes the relationship between AG and AG for this reaction?

Answer 1

Consider a reaction : 2 CH₃OH (l) + 3 O _2(g)   2 CO _2(g) +4 H₂O(l)

Consider a reaction: 2 CH_3OH (l) + 3 O_2 (g) Delta 2 CO_2 (g) + 4 H_2 O(l) For above reaction, Delta G_rxn^0 = Sum of Delta G_f^0 (products) - sum of Delta G_f^0 (Reactants) = 2 times Delta G_f^0 CO_2(g) + 4 times Delta G_f^0 H_2 O(l) - [2 times Delta G_f^0 CH_3 OH (l) + 3x Delta G_f^0 O_2 (g)] = (2 times -394.4) + (4 times -237.2) - [(2 times -166.4) + (3 times 0.000)] = -1737.6 + 332.8 = -1404.8 KJ/mol PART 2 Consider a given reaction, B_4C (s) Delta 4 B(g) + C(s) For above reaction, Q = (P_B)^4 We have relation, Delta G = Delta G_f^0 + RT ln Q = Delta G_f^0 + RT ln (P_B)^4 = Delta G_f^0 + 4 RT ln (P_B) ANSWER: Delta G = Delta G_f^0 + 4 RT ln (P_B)

For above reaction , G ⁰_rxn = Sum of G ⁰_f ( products ) - sum of G ⁰_f ( Reactants)

=2 x G ⁰_f CO _2(g) +4 x  G ⁰_f H₂O(l)  - [2 x G ⁰_f CH₃OH (l) + 3 x G ⁰_f O _2(g)  ]

=(2 x -394.4 ) + ( 4 x -237.2) - [ ( 2 x -166.4 ) + ( 3 x 0.000) ]

= -1737.6 + 332.8

= - 1404.8  KJ / mol

PART 2

Consider a given reaction , B₄C (s) $\rightleftharpoons$ 4 B (g) + C (s)

For above reaction , Q =( P _B ) ⁴  

We have relation, G = G ⁰_f +RT ln Q

= G ⁰_f + RT ln ( P _B ) ⁴  

= G ⁰_f + 4 RT ln ( P _B )

ANSWER : G = G ⁰_f + 4 RT ln ( P _B )