Consider the following equilibrium: N_2(g)+3H_2(g) rightleftarrows 2NH_3(g) Delt

Question

Consider the following equilibrium: N_2(g)+3H_2(g) rightleftarrows 2NH_3(g) Delta G degree= -34. kJ Now suppose a reaction vessel is filled with 8.96 atm of nitrogen (N_2) and 9.31 atm of ammonia (NH_3) at 863. degree C. Answer the following questions about this system: Under these conditions, will the pressure of NH_3 tend to rise or fall? rise fall Is it possible to reverse this tendency by adding H_2? In other words, if you said the pressure of NH_3 will tend to rise, can that be changed to a tendency to fall by adding H_2? Similarly, if you said the pressure of NH_3 will tend to fall, can that be changed to a tendency to rise by adding H_2? yes no If you said the tendency can be reversed in the second question, calculate the minimum pressure of H_2 needed to reverse it. Round your answer to 2 significant digits. atm

Explanation / Answer

since there is no H2 at starting some NH3 dissociates to form H2

Hence pressure of NH3 tend to fall

Adding H2 will reverse the tendancy , hence answer is Yes

given dGo = -34 KJ ,   = -34000 J

we have dGo = - RT ln K   where T = 863 C = 863+273 = 1136 K

-34000 J = -8.314 x 1136 x ln K

ln K = 3.6

K = exp ( 3.6) = 36.6

Kp = (pNH3)^2 / ( pN2 x pH2^3)

36.6 = ( 9.31^2 ) / ( 8.95 x pH2^3)

pH2 = 0.64 atm

Hence minimum oH2 to cause reversion is 0.64 atm

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