Question

For the reaction below, the thermodynamic equilibrium constant is K = 0.000708 at 30 °C.

NH₄CO₂NH₂(s) → 2 NH₃(g) + CO₂(g)

Suppose that 0.026 moles of NH₄CO₂NH₂, 0.052 moles of NH₃, and 0.026 moles of CO₂ are added to a 6.0 L container at 30 °C.

(a) What are Q and ΔG_R for the initial reaction mixture? Q= ______ ; ΔG_R= ______kJ/mol.

(b) Is there spontaneous reaction to the left or to the right?

(c) What is the total equilibrium pressure in the 6.0 L container at 30 °C? _______ bar.

[Hint for (c): Set up an I.C.E. (Initial, Change, Equilibrium) table and then show that the equilibrium partial pressure of NH3 will be two times the equilibrium partial pressure of CO2.]

Answer 1

a) Concentration of NH3 = 0.052/6 = 0.0086667M

Concentration of CO2 = 0.026/6 = 0.0043333 M

Concentration of NH4CO2NH2(s) = 0.0043333M

NH₄CO₂NH₂(s) → 2 NH₃(g) + CO₂(g)

0.00433333M       0.0086667 0.0043333M

Q = [0.0866667]^2[0.0043333] = 3.2548 * 10^(-5)

Delta G = -RTln(Q) = -(8.314)(303)ln(3.248*10^(-5)) = 26035.04 J/mol = 26.035 KJ/mol

b) The reaction is not spontaneous isince delta G is negative

c) Total equilibrium pressure

PV = nRT
P(6) = (0.052+0.026+0.026)(0.0821)(303)

P = 0.4311 atm