Best demonstration ever of Le Chatlier's principle.

Just in case someone wants to show this to a student or someone who's doubting.
In the course of my work, I had to dissolve some CaCO3 in acid. No real problem here, that works quite well. Giving off CO2. I was doing this in a plastic tube with a lid. To control the reaction, and keep bubbles from going over the side, I could close the lid. Shut down the reaction after maybe 15 seconds. No new bubbles form. When I opened the cap, there-1 a hiss of gas sometimes. and 2. the reaction starts dissolving the powder at the bottom. Lovely, self-contained, and I would think cheap.