This is known as the law of conservation of matter matter can neither be created nor destroyed, but matter simply changes form. New matter is never created, and no matter is ever destroyed. Na ions are in light blue and Cl ions are darker green for contrast.Īll reactions are simply rearrangements of matter in more stable ways. The sodium chloride crystal structure has each atom with six of its nearest neighbors in an octahedral geometric pattern. If we look at the crystal structure of NaCl, we notice that it is a closely packed cube. This can be understood by saying that two sodium atoms combine with one diatomic chlorine molecule to form two ionic units of sodium chloride.Īnother aspect of chemical reactions is the physical properties of compounds, or how atoms and molecules fit together. A more accurate way to correctly represent this reaction is as follows: This equation is not a balanced equation, and matter doesn’t just disappear and appear. Sometimes the arrow is read as “yields.” As you look at this equation, the natural question to ask is why are there three atoms on one side of the equation and only two atoms on the other? What happened to the extra chlorine atom? Good question. In the chemical equation above, the (s) stands for solid, and the (g) stands for gas which indicates which state of matter the substance is in. It can be read to mean that the reactants, sodium and chlorine, will react to form a single product, sodium chloride. The reactants are on the left hand side of the arrow and the product(s) is (are) on the right. The reaction can be symbolized in the following way: One example has already been given which is when sodium metal, a solid, combines with chlorine gas to form sodium chloride. This type of reaction combines two or more substances to form at least one new compound. The first is the simplest and is known as synthesis, or a composition reaction. There are four basic types of chemical reactions. One-half mole (O 2) 16 grams + One mole (H 2) 2 grams = 18 grams Balanced equations and chemical reactions One mole (C) 12 grams + One mole (O 2) 32 grams = 44 grams Here are some simple examples of the gram atomic weight for one mole of different common compounds. Using these mole ratios, you can substitute the grams for atomic mass units and calculate relative masses for reactants and products. The coefficient is given to determine the number of moles in the balanced equation. You need a very large number of atoms to be able to measure something you can see, like a teaspoon of salt. A mole is simply a very large number of atoms. A similar analogy is that a dozen bowling balls would weigh more than a dozen golf balls. Chlorine is much heavier than hydrogen because it has more protons and neutrons. An equal number of chlorine molecules would weigh 70 grams. 6.02 × 10 23 molecules of hydrogen would weigh 2 grams. Just like a dozen equals twelve, a mole equals Avogadro’s number of atoms or 6.02 × 10 23. With our knowledge of atomic structure and, since elements are known to bond in regular, predictable patterns in whole number ratios, there are a number of quantitative relationships that can be determined using information from the periodic table.Ī conveniently measured amount of any element that equals the mass in grams of that element is called a mole. This is a basic skill that will serve us well in the next lessons. We have reviewed the chemical naming rules and how to name any chemical, compound, or material based on a few important nomenclature protocols. At the conclusion of this lesson, you should be able to identify and describe any reaction and effectively balance both sides of a chemical reaction. We are now going to review the four different kinds of reactions and how to balance a chemical equation. ⬅ Previous Lesson Workshop Index Next Lesson ➡
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