Question

Consider the following reaction at 195 K:

2Cu2O (s) ----> 4 Cu (s) + O2 (g)

In one of your laboratory experiments, you determine the equilibrium constant for this process, at 195 K, is 5.060E-84. You are given a table of data that indicates the standard heat of formation (deltaHform) of Cu2O is -170 kJ/mol. Based on this information, what is the stnadard entropy change (deltaSrxn) for this reaction at 195 K? (answer in J/K). Show all work please!

Answer 1

ΔG^orxn

Given that T = 195 K

   K = 5.06 x 10^-84

ΔG^orxn = -RT ln K where R = 8.314 J/mol/K

            = - (8.314) (195) In (5.06 x 10^-84)

            = + 310945 J/mol

ΔH^orxn

ΔH^orxn = ΔH_f^o(products) - ΔH_f^o( reactants)

= 4 ΔG_f^o [Cu(s)] + ΔH_f^o [O2 (g) ] - { 2ΔH_f^o [Cu2O(s)]}

= 0 + 0 - { 2 x -170 kJ/mol }

= + 340 kJ/mol

= + 340000 J/mol

ΔH^orxn = + 340000 J/mol

ΔS^orxn:

ΔG^orxn = ΔH^orxn - T ΔS^orxn

+ 310945 = + 340000 - [(195) (ΔS^orxn)]

ΔS^orxn = + 149 J/mol