Why are masses conserved in a chemical change?

Answer 1

Conservation of matter is one of the tenets of physics, at least for non-nuclear reactions. Anytime energy is created in a chemical reaction, there is an infinitesimal loss of mass but it can't be detected in most lab equipment. Therefore, from the standpoint of classical physics, matter is always conserved in a chemical reaction.

Answer 2

Masss is not always conserved by a chemical change.
This law of thermodynamics has been changed to "the conservation of mass and energy". During a chemical change, some mass may be lost or gained by conversion to or from energy. For example, when gasoline burns, some of the mass is converted to heat energy, and used in a heat engine to power automobiles.

Answer 3

Cause the substances that react and those that result are made of chemical elements with a defined mass......and since you can only make appear new substances or make disappear old substances....but cannot create or delete elements in a reaction.....So it is a fact that the elements that enter and get out of a reaction are the same, both as nature and as quantity (number of atoms).....They just get mixed another way(old bonds are broken and new bonds between elements are formed)...in order to form new substances.....As a result.....the mass doesn't change

You probably wonder why the volume changes.....well volume is about number of molecules.....as you have probably noticed, you can have 3 kinds of reactions:

- reactions in which you can introduce one molecule and get more, for instance
2* NH3 ------> N2 + 3* H2
....in the reaction above you introduce 2 molecules of NH3 and get 1 molecule of N2 and 3 of H2 (1+3 = 4......you obtain 4 molecules, per total)......so, in this case, the final volume doubles

-reactions in which you introduce more molecules, and get less, like in the following:
2* H2 + O2 ------> 2* H2O
......you introduce 2 + 1 = 3 molecules (2 molecules of H2 and 1 molecule of O2) and got only 2 molecules of water......the volume decreases

-reactions in which the number of molecules that enter and that come out is constant....and so is the volume
CH3COOH + NaOH -------> CH3COONa + H2O
....1+1 = 2 molecules that enter......1+1= 2 molecules that come out

This is possible cause the substances that went into the reaction are not the same as the ones that came out.

Answer 4

Because of the Law of Conservation of Mass maybe?

Answer 5

Since matter cannot be created or destroyed. It's a chemical law.