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Law of Conservation of Mass - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

The law of conservation of mass states that mass is neither created nor destroyed. In a closed system, mass of reactants is equal to mass of products. The law of conservation of mass is related to the law of conservation of matter.

Alright so let's talk about the law of conservation of mass, the law of conservation of mass states exactly what it sounds like it should, mass is neither created or destroyed during a chemical change and it's conserved so we are only going to be able to change mass or change matter, we're not allowed to actually create matter out of nothing or destroy matter into nothing. Alright so how is this helpful in dealing with chemi- in dealing with chemical reactions, here's a scenario that we might use to employ the law of conservation of mass.

Alright let's say we have an experiment we have 10 grams of red mercury 2 oxide and it's placed in an oven flask and it's heated until all of it decomposes and it decomposes into it's elements mercury and oxygen and the liquid mercury has a mass of 9.26 grams, what is the mass that of oxygen that gas that is formed. Alright so we started off with a mass of 10 grams of mercury 2 oxide okay we're going to take this sign this is saying here are the reactants reacted to decomposing into its products we're going to say this is equal 2. We have mercury, mercury we measured in that's its 9.26 grams okay? And we wanted how much how much oxygen gas its given off, we don't know we also we do know that law of conservation of mass states we're not going to destroy any matter we can't create matter out of nothing so the same the mass on this side should equal the mass of the products, so we can just do a basic mathematical problem and subtract 9.26 from both sides and we come up with point 74 grams of oxygen gas that's given off okay so the law of conservation of mass is really easy and it's really it explains a simplest concept that we cannot create matter out of nothing we cannot destroy matter into nothing.