So we did this experiment today from Sandwich Bag Science Experiments. We put 1 tsp baking soda in a bag and 3oz of vinegar in a sealed sandwich baggy. Then we tipped the bag to mix the contents. My 11yo quickly passed the baggy to me saying "it's going to explode!" Lol! The baggy became very cold and expanded to its full limit with air.
This related to physical vs chemical changes, and endothermic vs exothermic reactions.