HOW THE CANDLE EXPERIMENT WORKS
When you mix baking soda and vinegar together, you produce carbon dioxide. The carbon dioxide is heavier than air, so it will sit in the bottom of the glass. When you pour the gas from glass onto the candle, you are pouring out the carbon dioxide, which will sink and displace the (oxygen-containing) air surrounding the candle with carbon dioxide.
HOW BLOWING OUT A CANDLE WORKS
When you blow out a candle, your breath contains more carbon dioxide than it did when you inhaled the air, but there’s still oxygen that can support wax combustion.
So, you may be wondering why the flame is extinguished. It’s because a candle needs three things to sustain a flame: fuel, oxygen, and heat. The heat overcomes the energy needed for the combustion reaction. If you take it away, the flame can’t sustain itself. When you blow on a candle, you force the heat away from the wick. The wax drops below the temperature needed to support combustion and the flame goes out.