Watch this video for a demonstration on the Law of Conservation of Mass So, the total mass of reactants equals the total mass of products, a proof of the law of conservation of mass. After the reaction is complete and the materials separated, we find that we have formed 143.4 grams of silver chloride and 85.0 grams of sodium nitrate, giving us a total mass of 228.4 grams for the products. If we react 58.5 grams of sodium chloride with 169.9 grams of silver nitrate, we start with 228.4 grams of materials. ![]() When we evaporate the water, we can recover the sodium nitrate formed. The silver chloride does not dissolve in water, so it forms a solid that we can filter off. These two compounds will dissolve in water to form silver chloride and sodium nitrate. In other words, mass cannot be created or destroyed during a chemical reaction, but is always conserved.Īs an example, consider the reaction between silver nitrate and sodium chloride. ![]() One of these is called the law of conservation of mass, which states that during a chemical reaction, the total mass of the products must be equal to the total mass of the reactants. Accurate and reproducible measurements of the masses of reacting elements and the compounds they form led to the formulation of several basic laws. In the 1790s, a greater emphasis began to be placed on the quantitative analysis of chemical reactions. There were questions about the details of these processes. The chemical and physical properties of these compounds are different than the properties of the elements from which they were formed. It was also clear that elements combine with one another to form more complex substances called compounds. Law of Conservation of Massīy the late 1700s, chemists accepted the definition of an element as a substance that cannot be broken down into a simpler substance by ordinary chemical means. You expect to end up with the same amount of material that you started with, not with more or less than what you had originally. ![]() In either case, you know something is wrong. Or you find out that a screw is missing that was a part of the original equipment. When you put the equipment back together, somehow you have an extra screw or two. You have taken apart a piece of equipment to clean it up. The following situation happens all too often. We also know that atoms can be further subdivided, but there is still a lower limit to how small we can break up that grain of sand. We now know more about how atoms hold together in “clusters” (compounds), but the basic concept existed over two thousand years ago. It is very interesting that Democritus had the basic idea of atoms, even though he had no experimental evidence to support his thinking. We had to wait almost two thousand years before scientists came around to seeing the atom as Democritus did. The theory of Democritus explained things better, but Aristotle was more influential, so his ideas prevailed. According to Aristotle, everything was composed of four elements: earth, air, fire, and water. When these atoms collided with one another, they might repel each other or they might connect in clusters, held together by tiny hooks and barbs on the surface of the atoms.Īristotle disagreed with Democritus and offered his own idea of the composition of matter. The void was the empty space in which the atoms moved and collided with one another. There was an infinite number of atoms, but different types of atoms had different sizes and shapes. ![]() The word “ atom ” comes from the Greek atomos and means “indivisible.” The atomists of the time (Democritus being one of the leading atomists) believed there were two realities that made up the physical world: atoms and void.
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