 
Kendra F. answered  01/12/17
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The law of conservation of mass states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. Basically, the law implies that matter cannot be created nor destroyed, although it can change form or rearrange.
Thus, during any chemical reaction, nuclear reaction, or radioactive decay in an isolated system, the total mass of the reactants or starting materials must be equal to the mass of the products.
A + B --> CD
75g + B --> 100g
100g - 75g = 25g
     
    