Source: Philpot Education
At first glance, some reactions may seem to violate the principle of conservation of mass. It's not always easy to measure all the matter involved in a reaction from the surrounding air, but how much? Likewise, the products escape into the air. Again, how much?
A fish bowl is an example of an open system. It contains different types of matter that are interacting with each other. In an open system, matter can enter from or escape to the surroundings. If you want to measure all the matter before and after a reaction, you have to be able to contain it. In a closed system, matter does not enter or leave. A chemical reaction that occurs inside a sealed, airtight container is a closed system.
