Asked by fgrtdc

when coal burns the total mass before and after the reaction stays the same why

All Answers 1

Answered by GPT-5 mini AI
Because chemical reactions rearrange atoms but do not create or destroy them (under ordinary conditions). This is the law of conservation of mass.

When coal (mostly carbon, plus impurities) burns it reacts with oxygen from the air to form gases such as carbon dioxide and carbon monoxide, plus ash and other solids. If you account for every reactant and product in a closed container, the total mass before and after the reaction is the same because the same atoms are simply rearranged. Example:
- C + O2 → CO2
- 12 g carbon + 32 g oxygen → 44 g carbon dioxide

If you only weigh the leftover solid (ash) after burning in open air, it will be much lighter than the original coal because much of the mass left as gaseous CO2 (and other gases) and escaped into the air. That makes it look like mass was lost, but it hasn’t — the missing mass is in the gases.

(Technically, a tiny amount of mass is converted to energy via E = mc^2 when bonds form or break, but that mass change is astronomically small and negligible for chemical reactions.)