Chemical Equilibrium

The Concept of Equilibrium and Equilibrium Constant

Chemical Equilibrium

            -is achieved when the rates of forward and reverse reactions are equal and the concentrations of the reactants and products remain constant

Physical Equilibrium

            -because the changes that occur are physical processes

Rate_forward=Rate_backward

 

Rules in Writing Equilibrium Constant

1.      1. [A] [B] [C] and [D] are molar concentrations in equilibrium. P_a, P_b, P_c, P_d  are equilibrium pressures in terms of atmosphere.

2.      2. The products are always in the numerator, and reactants are always in the denominator.

3.      3. The coefficients of the reactants and the products in the balanced equations correspond to their exponents for the expression.

4.      4. Compounds or molecules in a solid or liquid phase are ignored. They are not included in expression. 

5.      5. K_eq does not have a unit since it is an expression for a ration.

6.      6. Only substances in a gas phase are expressed in the K_p expression.

 

Writing Equilibrium Constants in terms of Pressure (K_p)

            K_c ≠ K_p         

            K_p

                    _-tells us that equilibrium  concentrations are expressed in terms of pressure