What is the law of conservation of mass?

No atoms are lost or made during a chemical reaction.

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In a chemical reaction, is there any change in the overall mass of the substances?

No. The overall mass of the products will be exactly the same as the overall mass of the reactants.

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Give 3 reasons why the total mass may appear to change during a chemical reaction. 

  1. Gases from the air may react with the chemicals in the beaker, increasing the mass.
  2. Gaseous products may escape from the beaker into the air, decreasing the mass.
  3. Some chemicals may be lost via spilling or evaporation, decreasing the mass.


(in exams it is best to put the first 2 answers)

Answer in your head, out loud, or on paper, then tap the card to flip.