Question

1. Chemical thermodynamics and chemical kinetics study two different aspects of
chemical reactions. Explain what these are and how they are related.
2. Describe some of the advantages of studying the mechanisms of chemical reactions.
3. Derive an expression for t½ for a second order reaction (Rate = k[A]2).

Answer 1

a)We know that the Kinetics and thermodynamics are related to each other. They are related in ways that can be explained by using chemical reactions. Thermodynamics is the study of energy changes accompanying physical and chemical changes. "thermo", it is a word from temperature, meaning energy, and "dynamics", which means the change over time. Chemical kinetic is the study of rate of chemical process. it includes the study of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states. Chemical kinetics is the study and discussion of chemical reactions with respect to reaction rates, effect of various variables, re-arrangement of atoms, formation of intermediates etc. We know that the study of motion is called kinetics, from Greek kinesis, meaning movement.

Kinetics is related to reactivity and Thermodynamics is related to stability.

b) It is important for many reasons, including

->It helps in understanding and controlling chemical reactions. Many reactions of great commercial importance can proceed by more than one reaction path; knowledge of the reaction mechanisms involved may make it possible to choose reaction conditions favouring one path over another, thereby giving maximum amounts of desired products and minimum amounts of undesired products.

->It is possible to find correlations between systems not otherwise obviously related. The ability to draw such analogies frequently makes it possible to predict the course of untried reactions.

->The detailed information about reaction mechanisms permits unification and understanding of large bodies of otherwise unrelated phenomena, a matter of great importance in the theory and practice of chemistry.

c) consider the reaction rate depends on the second power of the concentration of the single reactant. This type can be seen when the two molecule of the same reactant react in a single elementary reaction.

R+R=2R

Rate of reaction is

dR/dt=k[R][R]=k[R]^2

1[R]−1[R]01[R]−1[R]0 = kt

The half life period means the concentration of the reactant gets exactly halved. So

1/(1/2[R]₀)−1[R]₀=kt_1/2

This can be rewritten as

2/[R]₀−1/[R]₀ = kt_1/2

1/[R]o = kt_1/2
t1/2 = 1/([R]o×k)