Consider the decomposition of a metal oxide to its elements where M represents a
ID: 839845 • Letter: C
Question
Consider the decomposition of a metal oxide to its elements where M represents a generic metal:
M2O (s) -----------------------> 2 M (s) + 1/2 O2 (g) Delta Gf (kj/mol) for M2O, M and O = -6.00, 0, 0
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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) M2O(s) <=> 2 M(s) + 1/2 O2(g)
Delta Go = Delta Gf(products) - Delta Gf(reactants)
= 2 x Delta Gf(M) + 1/2 x Delta Gf(O2) - Delta Gf(M2O)
= 2 x 0 + 1/2 x 0 - (-6.00)
= 6.00 kJ/mol
(2) T = 298 K
R = 8.314 J/mol.K
K = exp(-Delta Go/RT)
= exp(-6000/(8.314 x 298))
= 0.0888 = 8.88 x 10^(-2)
(3) K = P(O2)^(1/2) = 0.0888
P(O2) = (0.0888)^2
= 0.00788 atm = 7.88 x 10^(-3) atm