Changes of Volume Associated with Transformations

The changes of volume observed during a chemical reaction are essentially the result of the volume demands of reactants and products. We will consider the reaction of pure or dissolved substances in order to calculate the effect at an 

The starting as well as the final substances may be present concurrently in large or small amounts and in pure or dissolved states. We assume the pressure and temperature to remain constant during the whole process in order to avoid unwanted effects caused by compressibility and thermal expansion. We also require that no other reaction runs in parallel, i.e.,, . are constant. A small extra conversion then results in the following change of volume (instead of Fm.g for a substance B, we use, as mentioned, the abbreviated Fg, etc.)  

Every product requires an additional volume A(J, while every reactant releases a volume A. denotes the required space of a given substance at 

Because the change of volume AV is proportional to the conversion (at least as long as A remains small), it is more useful to relate information of this kind to the conversion. Instead of AV, we use the quantity 

ArF( ) is the molar reaction volume which is the measure of how strongly the transformation of the substances taking place changes the volume at a particular extent of reaction. The index r refers to reaction and serves to differentiate the molar reaction volume (unit m mol ) from a change of volume AV (unit m ). 

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