In today's activity, we mixed two compounds, Sodium bicarbonate (Baking soda) NaHco3 and Acetic acid (Vinegar) CH3COOH in a large beaker. In the beaker was a burning candle. A chemical reaction occurred generating lots of bubbles. A few students noticed that the bottom of their beaker turned colder, indicating an endothermic reaction. The candle flame went out! The bubbles contained the gas Carbon dioxide, CO2. When the students went to relight the candle in the beaker, they were unable to. This was because the beaker was filled with the CO2. CO2 is heavier, or more dense, than air so it pushes the air out of the way. The air has Oxygen, O, in it. Without the Oxygen, you can't have a fire. Take a look at the video of this chemical reaction.