New Linux User has a very useful article about how to kill an application that misbehaves in your KDE.
When in KDE, if an application stops responding, just press Ctrl-Esc and it brings up the KDE process table. This table lists all the running processes and you just have to select the application that is not responding and have to click the kill button.
Actually, people say that Linux doesn’t hang like Windows. Yes, that is absolutely true, but the Graphical User Interface (desktop environment) has its own bugs and it is still not so stable to run any kind of app without crashing. Whatever happens to the desktop environment , you could always use the command line interface (CLI). CLI users always boast of this power and uninterrupted usage. This is also an important thing why Linux has better uptimes than Windows machines.