{"id":4374,"date":"2019-06-17T18:10:15","date_gmt":"2019-06-17T18:10:15","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/3-8-chemical-reactions-3\/"},"modified":"2023-11-30T17:50:46","modified_gmt":"2023-11-30T17:50:46","slug":"3-8-chemical-reactions-3","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/3-8-chemical-reactions-3\/","title":{"raw":"3.8 Chemical Reactions","rendered":"3.8 Chemical Reactions"},"content":{"raw":" \r\n

Is It Magic?<\/h1>\r\n[caption id=\"attachment_2296\" align=\"alignleft\" width=\"267\"]\"Chlorine Figure 3.8.1 Chlorine gas in high concentration.<\/em>[\/caption]\r\n\r\nThe harmless-looking bottle in Figure 3.8.1 contains a greenish-yellow, poisonous gas. The gas is chlorine, which is also used as bleach and to keep the water in pools and hot tubs free of germs. Chlorine can kill just about anything. Would you breathe in chlorine gas or drink liquid chlorine? Of course not, but you often eat a compound containing chlorine. You probably eat this chlorine compound just about every day. Can you guess what it is? It's table salt.\r\n\r\n[caption id=\"attachment_534\" align=\"alignright\" width=\"283\"]\"Image Figure 3.8.2 Table salt contains the elements sodium and chloride.<\/em>[\/caption]\r\n\r\nTable salt is actually sodium chloride (NaCl), which forms when chlorine and sodium (Na) combine in certain proportions. How does the toxic green chemical chlorine change into the harmless white\u00a0compound\u00a0we know as table salt? It isn't magic \u2014 it's chemistry, and it happens in a chemical reaction.\r\n
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What Is a Chemical Reaction?<\/h1>\r\n<\/div>\r\nA\u00a0[pb_glossary id=\"5729\"]chemical<\/strong>\u00a0reaction<\/strong>[\/pb_glossary]\u00a0is a process that changes some chemical substances into others. A substance that starts a chemical reaction is called a\u00a0[pb_glossary id=\"5501\"]reactant[\/pb_glossary],<\/strong>\u00a0and a substance that forms as a result of a chemical reaction is called a\u00a0[pb_glossary id=\"5503\"]product[\/pb_glossary].<\/strong>\u00a0During the reaction, the\u00a0reactants\u00a0are used up to create the products.\r\n\r\nThe burning of methane\u00a0gas, as\u00a0shown in the picture\u00a0below, is a\u00a0chemical reaction. In this reaction, the reactants are methane (CH4<\/sub>) and oxygen (O2<\/sub>), and the products are carbon dioxide (CO2<\/sub>) and\u00a0water\u00a0(H2<\/sub>O). As this example shows, a chemical reaction involves the breaking and forming of\u00a0[pb_glossary id=\"5505\"]chemical bonds[\/pb_glossary]<\/strong>, which\u00a0are forces that hold together the atoms of a molecule. When methane burns, for example, bonds break within the methane and oxygen molecules, and new bonds form in the molecules of carbon dioxide and\u00a0water.\r\n\r\n \r\n\r\n[caption id=\"attachment_581\" align=\"aligncenter\" width=\"508\"]\"Image Figure 3.8.3 Flames from methane burning.<\/em>[\/caption]\r\n\r\n
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Chemical Equations<\/h1>\r\n<\/div>\r\nChemical reactions\u00a0can be represented by chemical equations. A\u00a0[pb_glossary id=\"5507\"]chemical equation[\/pb_glossary]<\/strong>\u00a0is a symbolic way of showing what happens during a chemical reaction. The burning of methane, for example, can be represented by the chemical equation:\r\n\r\nCH4<\/sub><\/span>\u00a0+ 2<\/span>O2<\/sub><\/span>\u00a0\u2192 CO2<\/sub><\/span>\u00a0+ 2<\/span>H2<\/sub><\/span>O<\/strong>\r\n\r\nThe arrow in a chemical equation separates the reactants from the products, and shows the direction in which the reaction proceeds. If the reaction could occur in the opposite direction as well, two arrows pointing in opposite directions would be used. The number 2<\/strong><\/span> in front of O2<\/sub>\u00a0and H2<\/sub>O, called the coefficient<\/em>, shows that two<\/span><\/strong> oxygen molecules and two<\/strong><\/span> water molecules are involved in the reaction. If just one molecule is involved, no number is placed in front of the chemical symbol.\u00a0Note the subscript<\/em> of 2<\/strong><\/span> for the oxygen (O) and hydrogen (H) atoms in the oxygen and water molecules, respectively. That tells you that each oxygen molecule is made up of two<\/strong><\/span> oxygen atoms. If there is no subscript, then\u00a0there is a single\u00a0atom. Thus, one water molecule is made up of two hydrogen atoms and one oxygen\u00a0atom. In order for this\u00a0chemical reaction to take place, one methane molecule reacts with two oxygen molecules to form one carbon dioxide molecule and two water molecules.\r\n
\r\n\r\n[caption id=\"attachment_977\" align=\"alignright\" width=\"290\"]\"Shows Figure 3.8.4 Antoine Lavoisier is known as \"the father of modern chemistry.\"<\/em>[\/caption]\r\n

Conservation of Mass<\/h1>\r\n<\/div>\r\nIn a chemical reaction, the quantity of each\u00a0element\u00a0does not change. There is the same amount of each element in the products as there was in the reactants. Mass is always conserved. According to the\u00a0[pb_glossary id=\"5509\"]law of conservation of mass[\/pb_glossary]<\/strong>\u00a0\u2014\u00a0<\/strong>which was first demonstrated convincingly by French chemist Antoine Lavoisier<\/a> in 1785 \u2014 mass is neither created nor destroyed during a chemical reaction. Therefore, during a chemical reaction, the total mass of products is equal to the total mass of reactants.\u00a0The\u00a0conservation of mass\u00a0is reflected in a reaction's chemical equation. The same number of atoms of each\u00a0element\u00a0appears on each side of the arrow. In the chemical equation above, there are four hydrogen atoms on each side of the arrow. Can you find all four of them on each side of the equation?\r\n
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Chemical vs. Physical Changes<\/h1>\r\n<\/div>\r\nMany processes that happen all around us on a daily basis involve [pb_glossary id=\"5729\"]chemical reactions[\/pb_glossary]. Not every change, however, is a chemical change. Some changes are simply physical and do not involve chemical reactions. Physical changes include change in size of pieces and change in state.\u00a0 If you break an eggshell and pour out the egg into a pan, its chemical makeup and properties do not change. This is just a physical change. No chemical reactions have occurred, and no chemical bonds have broken or formed. Other examples of physical changes are cutting paper into smaller pieces and letting an ice cube melt. What if you put the egg in the pan over a hot flame? The egg turns to a rubbery solid and changes colour. The properties of the egg have changed because its chemical makeup has changed. Cooking the egg is a chemical change that involves chemical reactions.\r\n\r\nOther common examples of chemical changes include a cake baking, metal rusting, and a candle burning.\u00a0More practice is below.\r\n
\r\n\r\n[h5p id=\"462\"]\r\n\r\nFigure 3.8.5 Chemical changes often involve chemical reactions as well.\u00a0<\/em>\r\n
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3.8 Summary<\/h1>\r\n<\/header>\r\n
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