The Law of Conservation of Mass

As part of her chemistry class, Jess R. ('20), explored the law of conservation of mass. 

Scientist Antoine Lavoisier experimented burning different substances in air, and he observed that when these substances combined with air they made new materials which weighed more than the original substances. Lavoisier discovered that the reason the new materials weighed more was because the air in which the substances were burned had lost weight. The mass was not lost, rather it was transferred. Thus, Lavoisier established the Law of Conservation of Mass, this law states that mass can’t be lost or gained during a chemical reaction. This law applies to our everyday lives in so many different ways- we see it everywhere whether we are making dinner or balancing equations in science class. For instance, when you boil a pot of water with a lid and you see that some of the liquid is gone, you might wonder how it just disappeared. In reality the matter is not destroyed and it has not disappeared, it just changed phases. Some of the liquid water turns into water vapor as a result of heat being added to it, and the water vapor condenses on the lid of the pot. The mass is fully conserved, although it may take different forms after undergoing a chemical reaction. The mass of the system (pot, lid, water vapor, and liquid water) will be the exact same as the original mass of the system (pot, lid, liquid water). Lavoisier's law can also be applied to a burning fire. When wood burns in a fire, it reacts with oxygen and forms ashes, carbon dioxide, and water vapor. The gases disperse into the surrounding air, and all we can see are the ashes left behind. While it may look like mass has disappeared, if you measure the mass of the wood before it burned and the oxygen used by the fire it would be equal to the mass of the products left from the reaction. Lastly, this concept applies in a less literal way. As a kid after losing something you may have heard something along the lines of “well, it didn’t just disappear!” Nothing, large or small, solid or liquid or gas, can ever just disappear. Although you may not be able to see it, it still exists. This is because, as Lavoisier’s rule claims, matter cannot be created nor destroyed. You may have lost that little toy car in a pile of clothes, but if you massed everything in your room again collectively it would have the same mass as it did prior to losing a toy.

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