The Cambridge Chemical Engineering course treats the first year at University as a 'foundation year' in which students choose between studying first-year Engineering or first-year Natural Sciences.
The Engineering route gives students an excellent background in general engineering. It suits students who are particularly interested in applying science to solve real-world problems.
The Natural Sciences route gives students an excellent broad scientific background. It suits students who enjoy understanding how things work at a fundamental level. In the first year, students choose three scientific subjects from a choice of eight. In addition, they must also take a Mathematics option.
Note that one great advantage of the Cambridge system is its flexibility. You are not absolutely committed to reading Chemical Engineering even if you specify it on your application form. For instance, it is usually possible to continue studying a pure science if you do first-year Natural Sciences, or another branch of engineering if you do first-year Engineering. Cambridge is thus an ideal choice for University applicants who aren't quite certain which course they eventually want to study.