Question

Which law of chemical combination says that mass remains unchanged in a chemical change ?
(A) law of definite proportions
(B) law of multiple proportions
(C) law of conservation of mass
(D) law of reciprocal proportions​

Answer 1

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Which law of chemical combination says that mass remains unchanged in a chemical change ?

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C) Law of Conservation of mass

Explanation:

Law of Conservation of Mass Definition

The law of conservation of mass is that, in a closed or isolated system, matter cannot be created or destroyed. It can change forms but is conserved.

Law of Conservation of Mass in Chemistry

In the context of the study of chemistry, the law of conservation of mass says that in a chemical reaction, the mass of the products equals the mass of the reactants.

To clarify:

An isolated system is one that does not interact with its surroundings. Therefore, the mass contained in that isolated system will remain constant, regardless of any transformations or chemical reactions that occur—while the result may be different than what you had in the beginning, there can't be any more or less mass than what you had prior to the transformation or reaction.

The law of conservation of mass was crucial to the progression of chemistry, as it helped scientists understand that substances did not disappear as result of a reaction (as they may appear to do); rather, they transform into another substance of equal mass.

History credits multiple scientists with discovering the law of conservation of mass. Russian scientist Mikhail Lomonosov noted it in his diary as a result of an experiment in 1756. In 1774, French chemist Antoine Lavoisier meticulously documented experiments that proved the law. The law of conservation of mass is known by some as Lavoisier's Law.

In defining the law, Lavoisier stated, "Atoms of an object cannot be created or destroyed, but can be moved around and be changed into different particles."