I was also given computer applications for my second teaching subject when I applied for teaching at first. Even after I told the interviewers that I have no background and interest in this subject, I was still allocated this subject for contract teaching. In the end, i wrote an email to MOE HR to request for a change of second subject. I stated that I did not have any prior knowledge in this subject at all and I felt that it would be unfair to my students if I did not enjoy teaching it. I also suggested to them another second teaching subject which is more relevant to my tertiary studies (I even quoted the related module names in uni to show that I am more competent in this subject and also described how much passion I have for this subject instead (for you, maybe chemistry is a more suitable teaching subject).

But of course I guess everything is subjected to MOE’s needs but no harm trying. You can try to email them before you start contract teaching, if not everything will be cast and stone. All the best. Computer Applications is a subject taken by NT students, student management might be challenging and you might be given a NT form class more often because you are a Computer Applications teacher, but again depending on school’s needs.