To apply for the BS/MS program you follow this procedure:
1. Go to the Grad School website and go to the Admissions section and follow all instructions.
2. In your “areas of interest” on the form, put “accelerated masters”. This will signal that you’re applying for the BS/MS
All other application requirements for the BS/MS program are the same as for the MS program in general. For more on the BS/MS in Chemical Engineering, go to the Advising website FAQ page.
When you apply to graduate school you are most often asked to write a personal statement. There is some advice for this online; please take a look at this article from CrookedTimber.org.
My take is similar: be yourself, but your best self. Be honest; take some time to reflect on what your past experiences and choices have been.