Chemistry is a much more employable degree, showing both numerate\analytical skills as well as the ability to write a clear report. By contrast, history shows better literacy skills, but is no indication of numerical reasoning etc.
The workloads are very different on each degree. A chemistry student will have 20+ contact hours, spend a lot of time in the laboratory and have a lot of exams and theory to learn. A history student spends most of their time reading and writing essays, with few exams and contact hours. It is therefore much harder to stay motivated on a history degree, but you don't have the really horrible weeks where you just want to give it all up because you've had 12 contact hours and have another 5 or 6 of work to do (or at least not as many of those, anyway XD). This doesn't make history an easier ride, though, as the amount of reading required can seem superhuman at times.
My advice is to consider which subject you enjoy most, but if you really can't choose between them then I'd recommend chemistry - an interest in history is much easier to pursue as a leisure activity, and a chemistry degree brings with it many more, better options for employment.