Question

If the masses of all but one of the substances that take part in a chemical reaction are known, why is it possible to determine the unknown mass by subtraction?

Answer 1

Because mass is always conserved in a chemical reaction.......

Explanation:

So if I start with a 10 g mass of reactants, from all sources, AT MOST, I can get a 10 g mass of products. In practice, I am not even going to get that 10 g because losses always occur on handling.

All of this illustrates the principle of `"stoichiometry"`, i.e. `"GARBAGE IN EQUAL GARBAGE OUT"`.

For simple combustion reactions, e.g that of coal, I only need to know the starting mass of the coal. If the coal combusts completely, I know how much dioxygen is consumed as a reactant, and how much carbon dioxide is evolved:

`C(s) + O_2(g) rarr CO_2(g)`

If I combust 10 g of coal, how much carbon dioxide do I get out?

Is mass always conserved in a nuclear reaction? Why or why not?