Physical Chemistry

– In this topic, we will discuss the Catalysis and The types of catalysis : Homogeneous catalysis – Heterogenous catalysis. What is Catalysis? – Berzelius (1836) realised that there are substances which increase the rate of a reaction without themselves being consumed. – He believed that the function of such …

Collision theory of Reaction rates – According to collision theory, a chemical reaction takes place only by collisions between the reacting molecules. However, not all collisions are effective. – Only a small fraction of the collisions produce a reaction. – The two main conditions for a collision between the reacting …

Determination of the order of reaction – There are at least four different methods to determine the order of reaction as follows: Using integrated rate equations Graphical method Using half-life period The Differential method Ostwald’s Isolation method (1) Using integrated rate equations – The reaction under study is performed by …

Second order reaction – Let us take a second order reaction of the type 2A ⎯⎯→ products – Suppose the initial concentration of A is a moles liter–1. – If after time t, x moles of A have reacted, the concentration of A is (a – x). – We know …

First order reaction – Let us consider a first order reaction: A → products – Suppose that at the beginning of the reaction (t = 0), the concentration of A is a moles liter–1. – If after time t, x moles of A have changed, the concentration of A is …

– In this subject we talk about Molecular Vibrations as introduction to understand IR spectrum Molecular Vibrations – Before discussing characteristic infrared absorptions, it’s helpful to understand some theory about the vibrational energies of molecules. – The following drawing shows how a covalent bond between two atoms acts like a …

– we will discuss the Molecularity of a reaction and the Differences Between Order and Molecularity. Molecularity of a reaction – Chemical reactions may be classed into two types : (a) Elementary reactions (b) Complex reactions – An elementary reaction is a simple reaction which occurs in a single step. …

The Sulphur system –  Sulphur system is a one-component, four-phase system. – The four phases are: (a) Two solid polymorphic forms : Rhombic Sulphur (SR) Monoclinic Sulphur (SM) (b) Sulphur Liquid (SL) (c) Sulphur Vapour (SV) – All the four phase can be represented by the only chemical individual (sulphur) …

The Water system – Under normal conditions the Water system is a three-phase, one-component system. – The three phases involved are liquid water, ice, water vapour. – All these phases can be represented by one chemical entity H2O and hence one component of the system. – The number of phases …

Polymorphism – The occurrence of the same substance in more than one crystalline forms is known as Polymorphism. – Polymorphism phenomenon is shown by both elements and compounds. In the case of elements the term allotropy is often used. – The individual crystalline forms of an element are referred to …

Phase Diagram – A phase diagram is a plot showing the conditions of pressure and temperature under which two or more physical states can exist together in a state of dynamic equilibrium. – The following figure is a typical phase diagram for a one-component system. – The diagram consists of …

Derivation of the phase rule – Here the derivation of the phase rule for one-component system and two-component system are discussed. – Consider a heterogeneous system in equilibrium of C components in which P phases are present. – We have to determine the degrees of freedom of this system i.e., …

Degree of Freedom – The term Degree of Freedom represented by F in the phase Rule equation (F = C – P + 2) is defined as follows : the least number of variable factors (concentration, pressure and temperature) which must be specified so that the remaining variables are fixed …

The Phase Rule statement – The phase Rule is an important generalization dealing with the behaviour of heterogeneous systems. – In general it may be said that with the application of phase rule it is possible to predict qualitatively by means of a diagram the effect of changing pressure, temperature …

Applications of distribution law – There are numerous applications of distribution law in the laboratory as well as in industry. – Here we will discuss some more important ones by way of recapitulation. (1) Solvent Extraction – This is the process used for the separation of organic substances from aqueous …

Henry’s law statement – Henry’s law states: at a constant temperature the solubility of a gas in a liquid is proportional to the pressure of the gas above it. – Henry’s law may be mathematically expressed as C = kP where: C is the solubility (or concentration), k is a …

Introduction to Nernst’s Distribution Law – In this topic Nernst’s Distribution Law wlll be discussed – If we take two immiscible solvents A and B in a beaker, they form separate layers. – When a solute X which is soluble in both solvents is added, it gets distributed or partitioned …

Le Chatelier’s principle – In 1884, the French Chemist Henry Le Chatelier proposed a general principle which applies to all systems in equilibrium. This important principle called the Le Chatelier’s principle may be stated as : when a stress is applied on a system in equilibrium, the system tends to …

Calculation of Kc from Experimental Information – To determine the value of Kc of a reaction, write the balanced equation. Then write the equilibrium constant expression. – Substitute in it the equilibrium concentrations of the reactants and products found experimentally. Thus calculate the value of Kc. Solved problem (1) for …

Equilibrium constant: Equilibrium law – Now we will find the Expression of Equilibrium Constant. – Let us consider a general reaction A + B ↔ C + D – and let [A], [B], [C] and [D] represent the molar concentrations of A, B, C and D at the equilibrium point. …