Question

Why is it important to study chemical reactions in closed containers

Answer 1

 not to have anything that was not supposed to react with the chemicals in the container. I think.

Answer 2

When preforming a chemical reaction, it is crucial to keep it in a closed container.

Why is this?

A closed container is also known as a closed system. This means that what ever is inside the container does not react with anything OUTSIDE the container. Air, oxygen, or anything else could completely RUIN the reaction and you'll end up coming with weird, unexpected results.

So, open systems are commonly used for reactions.