Rate of reaction and stoichiometric coefficient 

Let’s consider a reaction N2 + 3H2      →         2NH3 The rate of reaction can be expressed as, Rate of disappearance of N2   =           Rate of disappearance of H2   =          Rate of disappearance of NH3     =  Here, during disappearance of 1 mole of N, 3 mols of H2 are […]

Instantaneous rate and average rate of reaction 

The rate of reaction at a point of time is the instantaneous rate of same reaction is different at different time. It is obtained from graph by drawing tangent at different point of time. The average rate of reaction gives the rate of reaction at large time interval. It is determined experimentally.

Chemical Kinematics 

Chemical Kinematics is a branch of physical chemistry that deals with determination of rate of reaction. A reaction proceeds with disappearance of a reacants and formation of products. So, the rate of a chemical reaction can be measured in terms of rate of disappearance of reactants and formation of products. Rate of reaction =    […]

Free energy change and net useful work 

Work other than pressure volume work (PΔV) is net useful work. So, total work of a process is, W = Wnet + PΔV Wnet = W – PΔV From Gibb’s helmuntz equation,            ΔG = H – TΔS      ……………. (i) We have,             H = E +   PΔV             S = Q /T             TΔS = […]

Criteria for spontaneity in terms of H, S and G 

ΔG,  ΔH and ΔS is related by Gibb’s – He/mhottz equation as,               ΔG = ΔH  – ΔS  The conditions under which different process are spontaneous is discussed as follows. a. Exothermic reaction with increase in entropy             for exothermic reaction,   ΔH = -ve             for increase in entropy,  ΔS = +ve             For […]

Second law of Thermodynamics 

The 2nd law of thermodynamics states, “All spontaneous process leads to the increase in entropy of the universe.” In case of isolated system, the change in entropy of the system is the total entropy change. So, the process will be spontaneous when the entropy of a system increases. In case of open system, the change […]

Entropy Function 

Entropy function was introduced by Clausius. Entropy of a system is the measurement of disorderness of randomness or chausness of the system. S = k ln w, where K = Bollzmann’s constant ln = loge w = no of probable arrangements   Entropy is a state function and depends only upon initial and final states, […]

Pseudo Unimolecular reaction 

In a chemical reaction if two or more reactants are involved but the rate of reaction depends only upon the concentration of one of the reactant and independent of other reactants then it is said to be pseudo unimolecular reaction.  Eg.            (i) Acid Catalyzed Hydrolysis of ester. (ii) Acid Catalyzed […]

Molecularity of a reaction 

Molecularity of a reaction is no of atoms, molecules or ions involved in collision to form product for simple reaction, molecularity is equal stoichiometric coefficient, but for complex reaction molecularity is no of atoms, ions or molecules involved in rate determining step i.e. slowest step. The molecularity is a theoretical value obtained from proposed reaction […]

Arhenius equation dependence of rate on temperature 

The variation of rate or reaction on temperature is given by Arhenius equation. This eqn is  k = A e– Eact/kt where            k = Rate constant            Eact = Activation energy             R = Universal gas constant             T = Temperature in Kelvin             A = […]