10: Chemical Reactions and Chemical Quantities
- Page ID
- 465562
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In this paragraph from the Elements of Chemistry, Antoine Lavoisier (1743–94) is explaining an experiment in which he was trying to demonstrate that water is not an element but instead is composed of hydrogen (the gas “capable of being burnt”) and oxygen. This is a historical account of a groundbreaking experiment and illustrates the importance of amounts in chemistry. Lavoisier was pointing out that the initial total mass of water and charcoal, 85.7 g plus 28 g, equals the final total mass of carbonic acid and the particular gas, 100 g plus 13.7 g. In this way, he was illustrating the law of conservation of matter - another way of saying that amounts matter.
Amounts do matter and in a variety of circumstances. For example, a nurse who mistakenly read “2–3 mg” as “23 mg” and administered the higher and potentially fatal dose of morphine to a child. Food scientists who work in test kitchens must keep track of specific amounts of ingredients as they develop new products for us to eat. Quality control technicians measure amounts of substances in manufactured products to ensure that the products meet company or government standards. Supermarkets routinely weigh meat and produce and charge consumers by the ounce or the pound.
In the lab, we look at changes in matter that deal with billions of atoms at a time. How can we keep track of so many atoms (and molecules) during the reaction process? In this chapter, we will be describing and quantifying chemical changes via stoichiometry - or "element counting".
Chapter Sections
- 10.1: Chemical Reactions and Balanced Chemical Equations
- In chemical reactions, atoms are not created or destroyed. The atoms that were present in the reactants are present in the products. They are merely reorganized into different arrangements in the products compared to the reactants.
- 10.2: General Types of Chemical Reactions
- Although there are untold millions of possible chemical reactions, most can be classified into a small number of general reaction types. Classifying reactions has two purposes: it helps us to recognize similarities among them, and it enables us to predict the products of certain reactions. A particular reaction may fall into more than one of the categories that we will define in this book.
- 10.3: Mole Quantities
- In order to determine the amounts of reactants and products that can be used/made in a chemical reaction based on their coefficient proportions, the amount of moles of each reactant available to react must found.
- 10.4: Stoichiometry
- The quantitative relationship among reactants and products is called stoichiometry. The term stoichiometry is derived from two Greek words: stoicheion (meaning "element") and metron (meaning "measure"). On this subject, you often are required to calculate quantities of reactants or products. Stoichiometry calculations are based on the fact that atoms are conserved. They cannot be destroyed or created. Numbers and kinds of atoms before and after the reactions are always the same. This is the basi
- 10.5: The Limiting Reactant, Theoretical Yield, and Percent Yield
- A stoichiometric quantity of a reactant is the amount necessary to react completely with the other reactant(s). If a reactant remains unconsumed after complete reaction has occurred, it is in excess. The reactant that is consumed first is the limiting reagent, which will determine the maximum possible amount of products made and minimum of excess reactant used.