Note: This guide is written for an Ubuntu-based system but should work on any Linux distribution running the Gnome desktop environment.
If a program stops responding in Linux, an easy way to kill it is with the xkill utility. This utility turns the mouse into crosshairs. Once the user clicks on a window with the crosshairs, said window is instantly killed. This is much more convenient than trying to find the process ID or name in a list of running processes and stopping it. In order to set up xkill with a keyboard shortcut, go to System -> Preferences -> Keyboard Shortcuts from your Gnome menu. Click the Add button on the bottom and create a new entry with the following information:
Click Apply to save the new entry. Now double-click on the right-hand side to assign a keyboard shortcut to this action. Hold down key combination you wish to use, for example, CTRL+ALT+ESC (Control + Alt + Escape). The new key combination will appear on the right:
Once this is done, you may close the Keyboard Shortcuts window. Try killing a program by holding down your shortcut combination and you should see crosshairs appear. To cancel the kill, simply click the right mouse button.