Hi. This is just a quick post about a trick to kill a not responding program without even having to find it's process id using terminal / system monitor. Just run ALT+F2 to launch "Run Application" (similar to WINDOWS+R in Windows) and type in "xkill" (without the quotation marks) and your mouse pointer / cursor will turn into an X pointer instead of arrow and just click on any program window that you want to kill. That's all. :)
P/S: Please be aware that when killing the program, all windows belongs to the process will be killed i.e multiple Google Chrome windows opened will be all closed.