Last night I was driving my 1996 volvo 850 and white smoke came out from under the passenger side of the hood. I added coolant because the resevoir was empty. The coolant bubbled a lot. This afternoon I checked the resevoir and it was empty again. Is this a blown head gasket?

It could be a blown head gasket or could be a stuck thermostat causing the coolant to bowel and the only place to go is out the resevoir bottle pull your oil dipstick check to see if you can see little water bubbles in the oil on the stick this kinda gives you an idea if the head gasket is blown because most of the time the coolant will mix with the oil if the thermostat is stuck close it will lead to a blown head gasket if you dont get it taken care of also you may have a slow leak in the water pump and once the level gets low its going to bowel whats left and the stem will come out the over flow tube on the bottle