Yes certainly it will work and for several hours. A 'standard' 9V battery is good for about 100 mAH or 50 Ma for 2 hours or... there are better methods I'd recommend a regulated switcher type 7.5V 1A Supply (Measured no load), that's what I use. A 9V switcher type would work as well but the linear regulator on the Arduino will run a little hotter... 125C is it's upper limit. I am reasonably sure that the data sheet I attached is the same as the Arduino or at least the same 'family' of regulators...
Good Luck in the Contest...
Bob
ALS1117.pdf (70 KB)