Consider the decomposition of a metal oxide to its elements where M represents a
ID: 1049393 • Letter: C
Question
Consider the decomposition of a metal oxide to its elements where M represents a generic metal: M2O3 (s) -----------------------> 2 M (s) + 3/2 O2 (g) Delta Gf (kj/mol) for M2O, M and O = -8.10, 0, 0 <------------------
1. What is the standard change in Gibbs energy for the reaction as written in the forward direction?
Delta Grxn = ? kj/mol
2. What is the equilibrium constant for this reaction as written in the forward direction at 298 K?
K = ?
3. What is the equilibrium pressure of O2 (g) over M (s) at 298 K?
PO2 = ? atm
Explanation / Answer
1. M2O3 (s) ----------------> 2 M (s) + 3/2 O2 (g)
DG0rxn = (3/2*Dg0O2+2*DG0M ) - (1*DG0M2O3)
= (3/2*-8.1+2*0)-(1*0)
= -12.15 kj/mol
2. DG0 = - RTlnK
-12.15*10^3 = -8.314*298lnk
K = equilibrium constant = 134.82
3. K = pO2^3/2
134.82 = x^(3/2)
x = equilibrium pressure of O2 (g) = 26.3 atm