Why couldn't mendeleev organize the entire periodic table during his research? question options: the elements showed no periodic properties. the atomic number was unknown at the time. some elements were undiscovered at the time. the atomic mass was unknown at the time.

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.