In the Regulations Governing Bachelor's and Master's Studies and in the electronic handbook of courses it is defined in which period the exam of each module takes place. With the booking of the module the student is automatically enrolled for the corresponding exam. 
For each module there is one date for the exam and second date for exam repetition (if needed). The dates of the exams are published on the MNF-Site.  

The timetables of the exams for Chemistry and Business chemistry can be found here:

Tables of Exams: Exams Fall Semester

Tables of Exams: Exams Spring Semester

Table of Exams: Exam Repetitions Fall/Spring Semester

If for any important reason somebody is not able to go to the exam after the deadline has expired, the respective student has to cancel the booking immediately at the Study Dean's Office.

The results of the exams can be seen in the student's own account under the summary of credit as soon as they are approved.

Exams which were not passed can be repeated once for each module in the following exam repetition period. An application for the repetition date is needed. If the exam is not repeated in the following exam period, the whole module has to be repeated.  A second repetition of a compulsory module is possible only once during the bachelor study and a written request for that has to be addressed to the Study Dean's Office.

For other proof of academic achievements, apart from module exams, the person in charge of the module is responsible. These persons define the modalities and requirements of the achievements, which will also be published in the course handbook (VVZ).