hi,

see in mechanical engineering and chemical engineering, engineering  mathematics and general aptitude is common to both of the syllabus, some of the same topics is fluid mechanics and heat transfer. I have given below the link to both the syllabus, you may check for clarity.

http://www.gate.iitg.ac.in/Syllabi/ME_Mechanical-Engineering.pdf

http://www.gate.iitg.ac.in/Syllabi/CH_Chemical-Engineering.pdf