i3wm open 2 applications with one keybinding?

Yes. You can chain i3 commands by passing a list, which is separated by either , or ;. For example, this will open a terminal and xclock on pressing Super+x:

bindkey Mod4+x exec i3-sensible-terminal; exec xclock

Note: while exec i3-sensible-terminal will be run before exec xclock, there is no guarantee that the window for i3-sensible-terminal will open before the window of xclock. That is due to the fact that exec does not wait for a window to be mapped before returning. (In fact it can not wait, as there is no way to know, if an application is even going to open a window.)

For more information about command chaining have a look at the i3 User's Guide