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# Tag Archives: Theory

## Principle of Equivalence Led to the Formulation of Einstein’s General Theory of Relativity

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The mass of a body, when subjected to a gravitational attraction but no acceleration (i.e., its gravitational mass) is the same when it is subjected to an acceleration but no gravitational attraction (i.e., its inertial mass).

This gave Einstein the idea that a gravitational field can be imitated by a field of acceleration and this, ultimately, led to the formulation of his general theory of relativity, wherein if showed that a non-accelerating or inertial frame of reference in which there is a gravitational field is physically equivalent to a reference frame accelerating uniformly with reference to the inertial frame but in which there is no gravitational field. This means, in other words, that experiments carried out in the two frames, under the same conditions, will yield identical results. This is called the Principle of Equivalence.

## The Lindemann Theory of Unimolecular Reactions

It is easy to understand a bimolecular reaction on the basis of collision theory.

When two molecules A and B collide, their relative kinetic energy exceeds the threshold energy with the result that the collision results in the breaking of comes and the formation of new bonds.

But how can one account for a unimolecular reaction? If we assume that in such a reaction $A \longrightarrow P$, the molecule A acquires the necessary activation energy for colliding with another molecule, then the reaction should obey second-order kinetics and not the first-order kinetics which is actually observed in several unimolecular gaseous reactions. A satisfactory theory of these reactions was proposed by F. A. Lindemann in 1922. (more…)