Chemistry question about unstoppered?

When you add sulphuric acid to any mixture that has carbonate salt, Carbon Dioxide is released. If you closed the flask with a stopper, the gas aculation inside results in higher pressure which could lead to the stopper being shot or the flask exploding. When you add Calcium chloride to the mixture, the results could be disastrous. Also during this reaction which is exothermic, a lot of heat is produced which is also another hazard if the flask is closed with a stopper.