The reaction which is in dynamic equilibrium, ensured us, that the reaction is reversible . But if that the reaction is in equilibrium. The reaction quotient predict either the reversiblereaction is in equilibrium or tries to achieve equilibrium. In those reactions which have not achieved equilibrium, we obtain reaction quotient Q_(c) in place of equilibrium constant (K_(c)) by substituting the concentration of reactant and product at the time, at whih we have to calculate the value of Q_(c) . To determine the direction at which the net reaction will proceed to achieve equilibrium, we compare values of Q_(c) and K_(c). The three possible cases are shown as comparison of K_(c) and Q_(c) in the following figures. Change in Gibbs free energy, i.e., Delta G is the driving force of any reaction. For spontaneous reaction , Delta G =-ve For non-spontaneous reaction , Delta G=+ve For reaction at equilibrium , Delta G =0 Thermodynamically, we know that Delta G= Delta G^(@)+ RTln Q, where Q is reaction quotient and Delta G^(@)= change in Gibbs energy at standard condition. For equilibrium A(g) hArr B(g) (K_(eq) =1.732) If the pressure of the system [varied by introducing a stream of A (g) and B (g) is representedby the curve at constant temperature T. For equilibrium system N_(2)O_(4)(g) hArr2NO_(2) (g) N_(2)O_(4)(g) is in a cylinder which is fitted with movable piston. Assume that equilibriumpartial pressureof N_(2)O_(4) (g)and NO_(2)(g) are 10 and 14 atmospheres respectively. If the piston of the cylinder is pulledout in such way so that volume of the system than what will be the value of equilibrium partial pressure of the NO_(2) gas ?