Question

Chemical Equilibrium and Equilibrium Constant

250 or more words please explaining.

Answer 1

When the concentration of all the reactants and products become constant, i.e; they do not change with time, the reaction is called in chemical equilibrium.

Characteristics of equilibrium:

(i)     It is dynamic in nature. Reaction takes place in both directions, even after achievement of equilibrium.

(ii)    The nature and properties of the equilibrium state are the same, regardless of the direction from which it is reached.

(iii)   All measurable properties of system remain constant over time.

EQUILIBRIUM   CONSTANT:

Consider a general reversible reaction: aP + bQ cR + dS

According to law of mass action, at any instant,

            Rate of forward reaction, r_f = k_f[P]^a[Q]^b

            And rate of backward reaction, r_b = k_b[R]^c[s]^d

At equilibrium, r_f = r_b

or, k_f [P]^a [Q]^b = k_b [R]^c [S]^d

or, k_f / k_b =  [R]^c [S]^d / [P]^a [Q]^b

Here, k_f / k_b = k_eq

or k = Equilibrium constant.

Reaction quotient of any reaction is the expression of equilibrium constant for that reaction, written for any state of reaction. For the above reaction,

the reaction quotient, Q = [R]^c_t [ S]^d_t / [P]^a_t [Q]^b_t

(i) The numerical value of Q for given reaction is variable. It depends on the concentration of products and reactants present at that time, when Q is determined. At the instant when pure reactants are mixed, Q is equal to zero, because [Product] = 0. As the reaction proceeds, the value of Q increases as the [Product] increases and [reactant] simultaneously decreases. When the reaction reached equilibrium, the value of the reaction quotient become equal to equilibrium constant.

· (ii) Direction of reversible reaction can be predicted from reaction quotient.

(a) If (Q < K), the amount of reactant will decrease and that of product will increase until Q = K i.e. reaction occurs mainly in the forward direction until the achievement of equilibrium.

(b) If (Q > K), the amount of reactant will increase and that of product will decrease until Q = K i.e. reaction occurs mainly in the backward direction until the achievement of equilibrium