Why is it so important to not return used or excess chemicals to their storage container?

There might be something that had reacted with the chemicals without us seeing it, so if you put it back in the same container it will react with other particles that may be in the container.

Some chemicals also have their chemical property changed upon contact of oxygen.

Just took the quiz on edgenuity and the correct answer is "c.  4.54 x  10–12  j"

Answer the same molecular formula;