The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:
Chemical kinetics is an important discipline in physical chemistry that deals with the rate & mechanism of chemical reactions. If you are working on solving a chemical reaction then you need to understand chemical kinetics first. Defined by its rate, chemical reactions can be fast, slow, or moderate. Many factors affect a reaction and make it slow or fast and thus altering the rate of the reaction. Chemical kinetics will help you in understanding the nature in which reactants react and their mechanism. In this article, you will learn the key concepts of Chemical kinetics and these notes will help you revise in the exams as well.
The rate of any particular reaction defines whether the reaction is fast, slow, or moderate. For example, magnesium ribbon when burnt with a bunsen burner immediately gets combusted making it a fast reaction. The rate of a chemical reaction can be expressed in the form of:
Assume that ‘R’ is the reactant & ‘P’ is the product & the volume of the system remains constant.
à P (chemical reaction of first order)
The rate of the above equation can be expressed as:
Rate of disappearance of R = Concentration decrease of R/Time Taken(t) = Δ[R]/Δt and similarly,
Rate of appearance of P = Concentration increase of P/Time taken(t) = Δ[P]/Δt.
The rate expressions can also be termed as integrated rate equations as they represent the concentration of products/reactants as a function of time (t).
Note: Δ[R] will be negative as the rate of reactants will always decrease to form products. You will have to multiply it with ‘-1’ to make the rate of reaction positive.
As you saw above, the rate expression of any reaction is expressed as the rate of change in concentration of reactant/product divided by the time taken. The unit of the rate expression will be concentration time -1.
If the concentration is measured in moles per litre & the time is measured in seconds in any rate expression, then the unit of the rate expression would be (mol L-1 s-1) where ‘mol’ is moles, ‘L’ is litres & ‘s’ is seconds.
The order of a reaction is said to be the sum of exponential value, i.e. the concentration of reactants in the rate law expression. For example, if the rate expression of any reaction is stated as:
Rate = k[A]1[B]1 where ‘A’ & ‘B’ are reactants, the order of this reaction will be the sum of coefficients, i.e. (1+1=2). We can also call this reaction a second-order reaction since its order is 2.
The molecularity of a reaction is defined as the number of reacting agents (atoms, ions, or molecules) in the reaction which must react to produce products. For example, in 2HI à H2 + I2, two different species are colliding simultaneously, thus making it a bimolecular reaction. The number of reacting species colliding simultaneously to complete a chemical reaction can also be termed as the molecularity of a reaction.
Half-life of Reactions
The half-life of a reaction is the time in which the concentration of the reactant is reduced to exactly half.
The rate of any reaction can change when subjected to a few factors. The factors influencing the rate of a reaction are:
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