Question

For the production of ammonia...`N_2(g)+3H_2(g) rightleftharpoons2NH_3(g)`..what is true at equilibrium...?

`"(1) The concentration of ammonia is "2.0*mol*L^-1`
`"(2) The concentration of dinitrogen is constant."`
`"(3) The concentration of ammonia is variable."`
`"(4) The concentration of ammonia cannot be determined."`

Answer 1

`(2)" the concentration of dinitrogen is constant"`

Explanation:

`N_2(g) + 3H_2 rightleftharpoons 2NH_3`

Chemical equilibria are a kinetic phenomenon, in that equilibrium unequivocally specifies that the RATE of the FORWARD reaction is EQUAL to the RATE of the BACKWARD reaction.

AS chemists, we can formalize this statement symbolically, `k_f` `=` `"forward rate constant"`; `k_r` `=` `"reverse rate constant"`, and thus:

`k_f[N_2][H_2]^3 = k_r[NH_3]^2` and,

`k_f/k_r=([NH_3][NH_3])/([N_2][H_2]^3)`, i.e.

`k_f/k_r=[NH_3]^2/([N_2][H_2]^3)`

The quotient `k_f/k_r` is more commonly referrred to as the equilibrium constant, `K_(eq)`, of the reaction. The concentration of products and reactants will alter UNTIL `K_(eq)` is satisfied and macroscopic change is no longer observed (of course, at the micro level change still occurs, but `K_(eq)` is satisfied.)

By the way, this equation represents probably one of the most important reactions of the planet. Dinitrogen reduction is exceptionally difficult to do, and without it we would have no nitrogenous fertilizer.

Also by the way, this is an important result to get your head around. If you have any objections or questions, voice them here, and someone will help you.