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Secondary II • 2yr.


I can't quite understand how the law of conservation of matter works. Can it be applied for both physical and chemical changes?

Thanks a lot!


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Explanations (1)

  • Explanation from Alloprof

    Explanation from Alloprof

    This Explanation was submitted by a member of the Alloprof team.

    Team Alloprof • 2yr.

    Thank you for your question😉

    To fully understand the law of conservation of matter, you must first understand one of the most important scientific principles, which states that "Nothing is lost, nothing is created, everything is transformed". What this sentence means is that during chemical reactions, no substance is created out of nothing and nothing disappears without reason; the initial material of a chemical reaction (the reactants) is simply transformed to obtain the products.

    This transformation works differently in a physical change and in a chemical change.

    In a physical change, the reactants and the products are the same, as no changes in the bonds between atoms occur. The initial molecules are the same as the final molecules. Only the shape or phase of the substance is changed. One can validate this idea by weighing a closed jar full of ice before and after the ice has melted. Since the mass doesn’t change, there is no change in the atoms. Nothing was lost and nothing was created.

    The idea is similar when it comes to chemical changes. The mass of the reactants and the mass of the products is the same, because no atoms are created nor destroyed. The only change that occurs is in the molecules’ bonds. They rearrange during the reaction to make molecules different from the initial ones. For example, in the below reaction, the atoms have only been rearranged to obtain products different from the reactants.

    $$2Cu + O{2} \rightarrow 2CuO$$

    Nothing was lost and nothing was created, the atoms were only transformed.

    If you have any other questions, don't hesitate to let us know! 😊

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