Like all engineers, chemical engineers use math, physics, and economics to solve technical problems. The difference between chemical engineers and other types of engineers is that they apply a knowledge of chemistry in addition to other engineering disciplines. Chemical engineers sometimes are called 'universal engineers' because their scientific and technical mastery is so broad.
http://chemistry.about.com/od/chemistrystudentfaqs/f/chemeng.htm
http://chemistry.about.com/od/chemistrystudentfaqs/f/chemeng.htm