It depends a lot on how good the signal is where you are. Plus, typically, although the phone will say 100% after you unplug the charger, it's probably a little under that and you'll see the number drop to 97% or 98% within a couple minutes.
When I'm connected to wifi (that turns off mobile data) and there are about 2 bars of cell/voice service, I burn about 2.5% an hour. If you're not on wifi, expect that burn rate to go up unless you're right next to a tower. LTE towers burn your battery faster than HSPA towers. Finally, if you have any apps that poll on a regular basis (email, facebook, twitter, etc.), that will use a little bit.
Say your starting point was actually 98% when you unplugged it, that means you burned about 5% in an hour and a half...that's around 3 to 3.5% an hour. If your cell service is weak-to-mediocre and you're not connected to wifi, then this burn rate seems perfectly reasonable. If you have GPS turned on, that could contribute, too. Make sure you turn that off when not in use.
And I agree with Photo4glover about the app killer. Don't install those: they're completely unnecessary and could do more harm than good (Android 2.1 and older had a tough time letting go of programs, that's why all those task killers exist.)