It is a solid...No, it is liquid....Watch out! It is a gas!
Small plastic bag with zipper top
Put the ice cube(solid) in the bag and close the top. Rub the bag in the palm of your hand to melt the ice. The ice can be placed in the sunlight or in warm water for faster results. The bag is now filled with water, which is a liquid. Open the bag and place an antacid tablet in the water. Reseal the bag and watch the gas form!
The antacid will dissolve and the bag will expand. When the antacid is placed into the water, carbon dioxide gas is formed. The bag could pop if two or three tablets are placed into the water. Be sure and wear your safety goggles! This is a great activity to demonstrate the states of matter.