Aircraft Equipment Problem Less Severe
Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft
Passing 10;500 feet on the arrival; slats were extended causing a pronounced roll.  The right hydraulic system quantity decreased to almost zero.  Pilot Flying continued to fly and talk to ATC; while Pilot Monitoring ran the R HYD Quantity low checklist.  Emergency was declared while running checklist.  We  were able to configure the aircraft to gear down and flaps 40.  An uneventful landing ensued.  Safety vehicles followed our aircraft to the gate.  A safety inspection was done by Safety Crew and Maintenance.   Emergency was terminated.
MD-82 pilot reports a pronounced roll when slats are extended; followed by the right hydraulic quantity going to zero.  An emergency is declared and the crew is able to land normally with full flaps and slats.