system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I burn 1kg of paper in a closed environment, will this environment be as heavy as before? If yes, why/how?
gpt
Yes, if by heavy you mean will it have the same amount of matter/energy. 

This is because burning is a chemical reaction that breaks the bonds between some atoms and creates new bonds with others. This produces heat and light, but doesn't change the number of atoms from beginning to end.