Hello,
Yes it should be compatible. Your Corsair CX500 PSU has 2x 6+2Pin PCI Express Power connectors, and the R9 280 Requires an 8 Pin and a 6 Pin
Verify on your power supply that you have 2x 6+2Pin Connectors before purchasing video card though, as you may have an older version of PSU.
Hope this Helps
^^^ i7Baby has a good point though that your power supply may be to low wattage...