https://community.linuxmint.com/tutorial/view/30
When you’re using Linux with the GNOME UI, don’t you hate it when you have to go into the terminal or add the force quit button to the panel just so you can exit an unresponsive program? In this very quick tutorial, I’m going to show you how you can assign the force quit command to a key, so when a program stops working, you can close it with the press of a button and a click of the mouse.
First, open up your GNOME menu and go to System > Preferences> Keyboard Shortcuts.
Second, click “Add” and a window should come up with 2 text boxes, labeled “Name” and “Command.” In Name, type “Force Quit” and in the Command box, type “xkill” and press Apply.
Scroll down to Custom Shortcuts in the Keyboard Shortcuts window and you’ll see Force Quit on the left side and Disabled on the right side. Click on Disabled once, and press a combination of keys on your keyboard. I used the Super (Windows logo) key and Escape, but you can use whatever you want, just as long as it doesn’t conflict any of your other shortcuts. Now Disabled will be changed to whatever keys you pressed.
Close out of the Keyboard Shortcuts window and you’re done! When ever you press your key combination, your cursor will change to crosshairs, or a skull and bones, or at least something different than just the arrow. Whatever window you click on will be forced to close, killing all of it’s processes.
If you find yourself to have accidentally pressed your force quit keys, then just right click and it’ll close out of the force quit mode.