Keyboard shortcut to open Google Chrome on Mac
If you don't want to use any third party applications you need to create a service and assign it a shortcut.
Open Automator and select Service. You want it to look like the following :
Save it to its default location. ie ~/Library/Services
Open System Preferences --> Keyboard --> Keyboard Shortcuts. Enable the service and assign it a shortcut.
Shortcuts for Automator services might not always work until the service has been selected once from the menu bar. And they won't be available in applications that don't have a Services menu. There's usually also a noticable delay before they are run.
Using a third party application like Alfred or Apptivate would probably be a better idea.
Another option would be assign shortcuts to AppleScripts like this:
tell application "iTunes" reopen activateend tell
Not with AppleScript alone -- there's no way to bind a keyboard shortcut to execute an arbitrary command.
Instead of writing something yourself, you may want to take a look at some existing launcher applications, like Butler, Spark, or Quicksilver.