Chemical Kinetics deals with the rate at which a chemical reaction occurs. Quite expectedly being a part of chemistry, rather physical chemistry to be precise, it deals with a lot of reactions and their properties that make things difficult for students to understand.
Mostly students find it hard to determine the reaction order, the rate constant, and the units of the rate constant. So, what makes them such a great deal?
Letâ€™s see what are the basic concepts of the terms that sum up whole of chemical kinetics.
Order of the reaction
Starting with reaction order solely based on the experiment and involves different methods to measure order. To determine the order of a reaction, the first method that is mostly chosen is that of method of initial rates.
So, what is initial rate method all about?
Method of initial rate is measured for a short time interval at the beginning of a reaction at several concentrations of the reactants.
In order to find the order of any reactions suppose, A Ã products
The rate law will be formulated as, Rate= k [A]n
Where, [A] = concentration of the reactant
k = kinetic constant
n = order of the reaction
Now, to find the order of a reaction, keep in mind the following tips:
- Check the unit of concentration
- Whether the reaction is stoichiometric or non-stoichiometric
- Check whether the rate of reaction is proportional to the concentration of the reactants.
Coming to the next topic,
Assuming a rate law,
Rate = k [A]m [B]n
Here, [A] and [B] are the concentration of reactants A and B.
â€˜mâ€™ and â€˜nâ€™ are order of reaction.
â€˜Kâ€™ is the rate constant.
Hence, the first thing to consider about rate constant is that it is not constant, rather is dependent on things like presence of catalyst, temperature etc. Hence, the rate law containing the constant k that is measureable and containing huge variations.
Few of the important tips to remember in case of rate constant is that-
- It is measureable and not constant as it depends upon temperature in presence of catalyst
- For the first order reaction, it varies in case of half-life that is independent of concentration and also includes concepts of radioactive decay.
- Rate constant and half life have inter-relation, as both of them are independent of the concentration.
Last but not the least,
Units of rate constant
The rate constant k has units and it is dependent upon the rate law. Different orders of reactions have different units of rate constant and rate laws. The simplest ones are- zero order, first order and second order reactions.
The unites are derived from the above reactions and hence it is important to consider the following rate laws,
- Zero order
Rate = k
- First order
Rate = k [A]
- Second order
Rate= k [A]2
These are some of the few tips that experts use to determine the reaction order, the rate constant, and the units of the rate constant. These are handy as well as quick to solve any problem regarding chemical kinetics.