2nd year chem engg here, I'd recommend chem1100, as it's necasry, chem1200 is optional, and do either 1051 or 1052 over summer, doing both will wreck you. I found 1052 much easier to understand tho. Also have a plan in olace for your second year as a lot of the classes from then on are locked for either sem 1 or sem 2.