Question

O ENTROPY AND FREE ENERGY Using reaction free energy to predict equilibrium compo.. Consider the following equilibrium: N, ()+ 3H2(g) - 2NH, () AGO-- 34. kJ Now suppose a reaction vessel is filled with 0.0559 atm of nitrogen (N2) and 8.61 atm of ammonia (NH) at 979. °C. Answer the following questions about this system: Under these conditions, will the pressure of NH, tend to rise or fall? 10 rise 0. x 5 ? Is it possible to reverse this tendency by adding H,? In other words, if you said the pressure of NH, will tend to rise, can that be changed to a tendency to fall by adding HSimilarly, if you said the pressure of NH, will tend to fall, can that be changed to a tendency to rise by adding H? If you said the tendency can be reversed in the second question, calculate the minimum pressure of H, needed to reverse it. Round your answer to 2 significant digits.

Answer 1

Under these conditions, will the pressure of NH₃ tend to rise or fall? : fall

Is it possible to reverse this tendency by adding H₂? : yes

minimum pressure of H₂ = 3.7 atm

Explanation

Given : $\Delta$ G^o = -34 kJ

ln(K_p) = -($\Delta$G^o) / (R * T)

where K_p = pressure equilibrium constant

R = constant = 8.314 J/mol-K

T = temperature = 979 ^oC = 1252 K

Substituting the values,

ln(K_p) = -(-34 x 10³ J) / [(8.314 J/mol-K) * (1252 K)]

ln(K_p) = 3.266

K_p = e^3.266

K_p = 26.2

K_p = [pNH₃]² / [pN₂][pH₂]³

26.2 = (8.61 atm)² / (0.0559 atm) * [pH₂]³

[pH₂]³ = (8.61 atm)² / [(0.0559 atm) * 26.2]

[pH₂]³ = 50.6

[pH₂] = (50.6)^1/3

[pH₂] = 3.7 atm