Chapter 1: Equilibrium

Study Material

Notes Part 1

Notes Part 2

Notes Part 3

Notes Part 4

Excercises 1

Excercises 2

Excercises 3

Excercises 4

As any reaction proceeds, [reactants] decreases and [products] increases.

Reversible reaction: a reaction which can go both ways.

Equilibrium: is the point when the [reactants] and [products] becomes constant.

Equilibrium: is the point when the [reactants] and [products] becomes constant.

Equilibrium is recognized by constancy of macroscopic properties in a closed system at

constant temperature.

Macroscopic properties are observable properties or measurable properties like pressure,

concentration, color, size, volume and mass.

Macroscopic properties are observable properties or measurable properties like pressure,

concentration, color, size, volume and mass.

Each set of equilibrium concentrations is called an equilibrium position.

Steady state: indicates a situation where macroscopic properties are constant but

equilibrium does not exist as the system is not closed e.g a blue Busen burner flame.

Equilibrium in physical changes: Solubility of iodine

Vapor pressure of water

Equilibrium in chemical reactions: NO2-N2O4 system

Equilibrium is dynamic in nature since at equilibrium two microscopic processes are

occurring in opposite direction at the same rate resulting in no observable macroscopic

changes.

Equilibrium is dynamic in nature since at equilibrium two microscopic processes are

occurring in opposite direction at the same rate resulting in no observable macroscopic

changes.

Equilibrium is dynamic in nature since at equilibrium two microscopic processes are

occurring in opposite direction at the same rate resulting in no observable macroscopic

changes.

Adding a catalyst or a noble gas does not alter the state of equilibrium.

Equilibrium may not reached in certain equilibrium system because the activation

energy of the forward reaction is too high.

Le Chatelier's Principle: if an equilibrium system is subjected to a change processes will

occur to partially counteract the imposed change.

Low temperature is required in the Haber Process for a desirable good yield and high

temperature is necessary for a satisfactory rate. The compromise used industrially

involves an intermediate temperature around 450°C and even then the success of the

process depends upon the presence of a suitable catalyst to achieve a reasonable

reaction rate.

High pressures are required in the Haber Process for a good yield and a satisfactory

high rate. It is expensive and dangerous to build up a pressure. A pressure of 200 atm is

actually used as a compromise.

Mass Action Expression: For a general reaction: αA + βB ⇆ ΥC + ΔD

Mass action expression = Q = [C]γ[D]Δ[A]/α[B]β

At equilibrium: mass action expression is constant and is given a special name, equilibrium

constant, Keq

Concentrations of solids and liquids are NOT included in the equilibrium expression.

These values are constant and are incorporate in the value of Keq directly.

Temperature and the nature of solvent are the only values which determine the value of

the equilibrium constant.

There is only one equilibrium constant for a particular system at a particular temperature

but there are an infinite number of equilibrium positions

Significance of value of K

If reactants and products are mixed are mixed, three things may occur:

 An equilibrium is established

 A reaction occurs in the forward direction

 A reaction occurs in the backward direction.

To find out what is occurring one needs to find the value of the mass action expression, Q

and compare it to Keq.

a. If Q >Keq reaction is NOT at equilibrium the backward reaction is taking place

(system shifts to the left).

b. If Q = Keq reaction is at equilibrium No shift occurs.

c. If Q <Keq reaction is NOT at equilibrium the forward reaction is taking place (system

shifts to the right).