[walterk01]

To stop/kill any app via the terminal use "Ctrl+c" while the terminal window is open.
If its been closed it should stop but if not run system monitor (System->Administration->System Monitor or Alt+F2 then type "gnome-system-monitor" without the quotes) search for the process in the Processes tab and either Kill or End it, this is the linux version of windows Ctrl+Alt+Del
Theres also a cmd you can use from the terminal to end or kill processes that are already running but you need to know the exact process ID number and cant just kill it by app name "kill -9 process id" to get the exact id you can run from the terminal "ps aux" which will list every process currently running , and the user it belongs to. Its going to be a long list and the ID number will be next to the username.