(1) Concurrency and program analysis are intesting research topics to me.

(2) CS is more thinking-heavy, at least in the subfield that I have stepped in (formal methods). During most of the time, we prove theorems, design algorithms and read papers. Only when every theorem is clear, we begin to do experiments. Chemistry is more about experiments, so that one needs to spend a lot of time working in the wet lab. Sometimes the same experiments have to be repeated for many times, simply because you have used up the materials you synthesized earlier. Usually these experiments are very tedious and don't require much thinking. The experiments are always there and it just needs somebody to do them.

(3) Some practical reasons: Averagely a CS graduate can earn more than chem. Computer Science is safer than chemistry, because in the worst case, you only crash your computer. In chemistry, things can be far more dangerous. See this link for an example.