The information entropy is one of the useful indices which can express degree of uncertainty about occurrence of phenomena and, in generally, it has been said that the natural phenomena move to the state in which the information entropy takes the maximum value. However, the information entropy has been scarcely used in the chemical engineering field, though there are many phenomena which can be understood by probability terms in the field. In addition, each index which is used in the field is defined independently of other indices and it can be said that there is no consistency of way of definition in the indices for close phenomena. In this article, it is tried to introduce the information entropy in order to define several main indices or to investigate a few important phenomena in the chemical engineering field and the usefulness of the information entropy is made clear by showing newly valuable information which are obtained through this discussion.