{"id":4345,"date":"2017-07-29T02:21:22","date_gmt":"2017-07-29T06:21:22","guid":{"rendered":"https:\/\/www.chemicool.com\/elements\/?page_id=4345"},"modified":"2017-12-07T02:07:39","modified_gmt":"2017-12-07T07:07:39","slug":"chemical-reactions","status":"publish","type":"page","link":"https:\/\/www.chemicool.com\/elements\/chemical-reactions.html","title":{"rendered":"Chemical Reactions"},"content":{"rendered":"<div class=\"author\">By Dr. Doug Stewart<\/div>\n<h3>How important are chemical reactions?<\/h3>\n<p>Long ago, people discovered that:<\/p>\n<ul>\n<li>substances can react to make new substances<\/li>\n<li>these reactions can be controlled<\/li>\n<\/ul>\n<p>The science of chemistry began when people began experimenting with chemical reactions systematically and organizing their results logically.<\/p>\n<p>As chemistry developed, scientists learned that <strong>living things exist only as a result of chemical reactions<\/strong> &#8211; and this includes you and me. <\/p>\n<p>Every living thing is a remarkably well-organized, self-managing chemistry set.<\/p>\n<div id=\"attachment_319\" style=\"width: 410px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-319\" src=\"\/\/www.chemicool.com\/images\/frogs-chem-kit.jpg\" alt=\"frogs\" width=\"400\" height=\"334\" class=\"size-full wp-image-319\" \/><p id=\"caption-attachment-319\" class=\"wp-caption-text\">Sophisticated chemistry sets?<\/p><\/div>\n<p>Our high-tech society could not exist without the ability of chemists to precisely control chemical reactions &#8211; the screen you&#8217;re viewing right now is one example of a device that would be impossible to make. <\/p>\n<p>So, on a one-to-ten scale of scientific importance, chemical reactions rate ten.<\/p>\n<div class=\"adsense340\">\n<img decoding=\"async\" alt=\"\" src=\"\/\/www.chemicool.com\/ad.png\"\/><br \/>\n<script async src=\"\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js\"><\/script><ins class=\"adsbygoogle\" style=\"display:inline-block;width:336px;height:280px\" data-ad-client=\"ca-pub-9461632227417539\" data-ad-slot=\"3265846807\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script>\n<\/div>\n<h3>People started reacting chemicals a long time ago<\/h3>\n<p>Our ancient ancestors learned:<\/p>\n<ul>\n<li>How to harness and control the oxygen-wood reaction to make fire.<\/li>\n<li>How to release metals from their ores to make efficient plows, axes, hammers and chisels.<\/li>\n<li>How to disinfect\/fumigate rooms and buildings with sulfur dioxide, the gas released by burning sulfur.<\/li>\n<li>How to convert limestone into calcium oxide, the basis of cement and concrete. Large-scale construction projects such as ancient Rome&#8217;s Colosseum became possible.<\/li>\n<\/ul>\n<div id=\"attachment_322\" style=\"width: 440px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-322\" src=\"\/\/www.chemicool.com\/images\/colosseum-day.jpg\" alt=\"The Colosseum , Rome\" width=\"430\" height=\"312\" class=\"size-full wp-image-322\" \/><p id=\"caption-attachment-322\" class=\"wp-caption-text\">The Colosseum was built using calcium oxide cement. This building is almost 2000 years old. Image by Paul Zangaro<\/p><\/div>\n<h4 style=\"color:red;\">Not all uses were peaceful<\/h4>\n<p>Our ancestors used new materials, such as iron and steel, to wage war. They discovered explosive chemical reactions and made gunpowder by mixing potassium nitrate, carbon, and sulfur.<\/p>\n<h3 class=\"greenbold\">We&#8217;re still making new discoveries<\/h3>\n<div id=\"attachment_329\" style=\"width: 132px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-329\" src=\"\/\/www.chemicool.com\/images\/mobile.png\" alt=\"Mobile technology depends on chemistry, from the plastics of the structure to the high energy density lithium batteries that provide power.\" width=\"122\" height=\"197\" class=\"size-full wp-image-329\" \/><p id=\"caption-attachment-329\" class=\"wp-caption-text\">Mobile technology depends on discoveries made by chemists &#8211; from plastics to lithium-ion batteries.<\/p><\/div>\n<p>Although we know a lot more about chemistry than our ancestors did, we continue studying chemical reactions; this brings improvements in technology and our health.<\/p>\n<p>The sheer excitement of making new discoveries also drives chemists to continue investigating reactions. Examples include:<\/p>\n<ul>\n<li>Lithium chemical reactions power our phones, tablet computers and cameras.<\/li>\n<li>Biochemical and electrochemical reactions enable our brains to store memories and to think.<\/li>\n<li>New chemical and biochemical reactions to produce new antibiotics, because bacteria are becoming increasingly resistant to the antibiotics we&#8217;re using today.<\/li>\n<\/ul>\n<h2>Reactants and Products<\/h2>\n<p>Chemical reactions begin with <strong>reactants<\/strong> and end with <strong>products<\/strong>. In chemical reactions:<\/p>\n<div style=\"text-align:center; font-size:1.4em; margin-bottom:30px;\"> reactants   &#8594;  products<\/div>\n<p>Using the right-pointing arrow above implies that all reactants turn into products. For example, we can make water by reacting hydrogen with oxygen. The reactants are hydrogen and oxygen. The product is water in the gas phase because the reaction produces a lot of heat.<\/p>\n<div style=\"text-align:center; font-size:1.4em; margin-bottom:30px;\">H<sub>2 (gas)<\/sub> + O<sub>2 (gas)<\/sub>   &#8594;  H<sub>2<\/sub>O<sub> (gas)<\/sub><\/div>\n<p>Often chemical reactions result in an <a href=\"https:\/\/www.chemicool.com\/definition\/equilibrium.html\">equilibrium<\/a> in which the reaction proceeds in both directions, leading to a mixture of reactants and products.<\/p>\n<p>This is shown using a different arrow:<\/p>\n<div style=\"text-align:center; font-size:1.4em; margin-bottom:30px;\"> reactants   &#8652;  products <\/div>\n<p>For example, the gas phase reaction used to make ammonia from hydrogen and nitrogen results in an equilibrium:<\/p>\n<div style=\"text-align:center; font-size:1.4em; margin-bottom:30px;\">N<sub>2 (gas)<\/sub> + 3H<sub>2 (gas)<\/sub> &#8652; 2NH<sub>3 (gas)<\/sub><\/div>\n<p>At equilibrium the <a href=\"https:\/\/www.chemicool.com\/elements\/chemical-reaction-rates.html\">reaction rates<\/a> in the forward and reverse directions are equal.<\/p>\n<h2>How do we know there&#8217;s been a chemical reaction?<\/h2>\n<div class=\"thinkbox\">\n<div class=\"think\">\nDid you know?<\/div>\n<div class=\"thinkimage\">\n<img loading=\"lazy\" decoding=\"async\" src=\"\/\/www.chemicool.com\/images\/thinknote.png\" width=\"60\" height=\"95\" alt=\"\"\/><\/div>\n<div class=\"thinktext\">\nFireflies glow when a chemical reaction in their bodies releases light.<\/div>\n<div style=\"margin:2px 16px 0 16px;\">\n<img loading=\"lazy\" decoding=\"async\" src=\"\/\/www.chemicool.com\/images\/firefly.jpg\" width=\"120\" height=\"141\" alt=\"Firefly glowing\" \/><\/div>\n<div class=\"thinktextc\">Firefly by Yikrazuul<\/div>\n<\/div>\n<p>There has been a chemical reaction <strong>only when one or more new substances are made<\/strong>. Sometimes this is obvious, sometimes less so. <\/p>\n<p>You will also <strong>often detect an energy change<\/strong>, because the reaction will heat up or cool down.<\/p>\n<h3>Example<\/h3>\n<p>Food can react chemically with oxygen. Two ways of reacting food with oxygen are <strong>burning<\/strong> and <strong>respiration<\/strong>.<\/p>\n<p>If the food is a carbohydrate, the word equation for both burning and respiration is:<\/p>\n<div style=\"text-align:center; font-size:1.4em; margin-bottom:30px;\">carbohydrate + oxygen   &#8594;  carbon dioxide + water<\/div>\n<p><strong>Burning<\/strong><br \/>\nThe ash and flame make it obvious that new substances are being made and that energy has been released. Ash forms because food usually doesn&#8217;t burn cleanly. Although the carbon dioxide and water formed by the reaction are less obvious, the ash and flame make it easy to tell that a chemical reaction has taken place.<\/p>\n<p><strong>Respiration<\/strong><br \/>\nThe evidence for a chemical reaction during respiration is more subtle than when we burn food. It&#8217;s not obvious that water and carbon dioxide are made by the reaction, although we can detect them. For example, we can use limewater to show that there is more carbon dioxide in the air we breathe out than in the air we breathe in. Breathing on a cold window produces condensation, indicating water is present in our breath. The energy released by respiration keeps all animals on our planet moving and keeps warm-blooded animals warm.<\/p>\n<h2>Signs of a chemical reaction<\/h2>\n<p>Look for one or more of these:<\/p>\n<h3>Appearance Changes<\/h3>\n<table class=\"greentable\">\n<tr class=\"alt\">\n<td>Gas is released <img loading=\"lazy\" decoding=\"async\" src=\"\/\/www.chemicool.com\/images\/check.png\" width=\"20\" height=\"20\" alt=\"check\" class=\"alignright\" \/><\/td>\n<\/tr>\n<tr class=\"alt\">\n<td>A solid appears or disappears <img loading=\"lazy\" decoding=\"async\" src=\"\/\/www.chemicool.com\/images\/check.png\" width=\"20\" height=\"20\" alt=\"check\" class=\"alignright\" \/><\/td>\n<\/tr>\n<tr class=\"alt\">\n<td>There is a color change <img loading=\"lazy\" decoding=\"async\" src=\"\/\/www.chemicool.com\/images\/check.png\" width=\"20\" height=\"20\" alt=\"check\" class=\"alignright\" \/><\/td>\n<\/tr>\n<\/table>\n<div style=\"height:30px;\"><\/div>\n<h3>Energy Changes<\/h3>\n<table class=\"greentable\">\n<tr class=\"alt\">\n<td>The temperature changes <img loading=\"lazy\" decoding=\"async\" src=\"\/\/www.chemicool.com\/images\/check.png\" width=\"20\" height=\"20\" alt=\"check\" class=\"alignright\" \/><\/td>\n<\/tr>\n<tr class=\"alt\">\n<td>Light\/flames seen <img loading=\"lazy\" decoding=\"async\" src=\"\/\/www.chemicool.com\/images\/check.png\" width=\"20\" height=\"20\" alt=\"check\" class=\"alignright\" \/><\/td>\n<\/tr>\n<tr class=\"alt\">\n<td>Sound is heard <img loading=\"lazy\" decoding=\"async\" src=\"\/\/www.chemicool.com\/images\/check.png\" width=\"20\" height=\"20\" alt=\"check\" class=\"alignright\" \/><\/td>\n<\/tr>\n<\/table>\n<div style=\"height:30px;\"><\/div>\n<p><span class=\"red\"><strong>The signs above are all clues, but (except for flames) don&#8217;t prove there has been a reaction. <\/strong><\/span><\/p>\n<p><strong>Remember:<\/strong><br \/>\n<span class=\"red\"><strong>A chemical reaction has happened only if one or more new substances are made. <\/strong><\/span><\/p>\n<div class=\"nonh2gray\">Test your knowledge:<\/div>\n<div class=\"nonh2\">Question 1<\/div>\n<p>Here is an example of a chemical reaction. Identify the reactant(s) and the product(s).<\/p>\n<div style=\"text-align:center; padding: 16px 0 22px  0; color:#333;\">\nsodium + chlorine   &#8594;  sodium chloride<\/div>\n<span class=\"collapseomatic \" id=\"id69eb9d9959702\"  tabindex=\"0\" title=\"Show Answer\"    >Show Answer<\/span><div id=\"target-id69eb9d9959702\" class=\"collapseomatic_content \">\nThe reactants are sodium and chlorine. The product is sodium chloride.<br \/>\n<\/div>\n<div class=\"nonh2\">Question 2<\/div>\n<p>You toast some bread and end up burning it. Has there been a chemical reaction? Why?<\/p>\n<span class=\"collapseomatic \" id=\"id69eb9d9959767\"  tabindex=\"0\" title=\"Show Answer\"    >Show Answer<\/span><div id=\"target-id69eb9d9959767\" class=\"collapseomatic_content \">\n<div class=\"thinktext\">Yes, there has been a chemical reaction, because when you burn toast, the color changes and a new substance forms. (The carbohydrate you started with reacts with oxygen and forms carbon.)<\/div>\n<div class=\"thinktext\">Note:  When anything burns, there is <strong>always<\/strong> a chemical reaction.<\/div>\n<\/div>\n<div class=\"nonh2\">Question 3<\/div>\n<p>A tree grows a little higher. Has there been a chemical reaction? Why?<\/p>\n<span class=\"collapseomatic \" id=\"id69eb9d99597a3\"  tabindex=\"0\" title=\"Show Answer\"    >Show Answer<\/span><div id=\"target-id69eb9d99597a3\" class=\"collapseomatic_content \">\n<div class=\"thinktext\">Yes, there has been a chemical reaction, because trees and other green plants grow by photosynthesis. During photosynthesis, green plants use energy from the sun to chemically combine water and carbon dioxide into carbohydrates such as cellulose and starch, while releasing oxygen gas.<\/div>\n<\/div>\n<div class=\"nonh2\">Question 4<\/div>\n<p>Name three visual clues that a chemical reaction might have happened.<\/p>\n<span class=\"collapseomatic \" id=\"id69eb9d99597d6\"  tabindex=\"0\" title=\"Show Answer\"    >Show Answer<\/span><div id=\"target-id69eb9d99597d6\" class=\"collapseomatic_content \">\n<div class=\"thinktext\">Gas is released<\/div>\n<div class=\"thinktext\">A solid appears or disappears<\/div>\n<div class=\"thinktext\">There is a color change<\/div>\n<\/div>\n<div class=\"nonh2\">Question 5<\/div>\n<p>When water freezes, has there been a chemical reaction? Why?<\/p>\n<span class=\"collapseomatic \" id=\"id69eb9d9959806\"  tabindex=\"0\" title=\"Show Answer\"    >Show Answer<\/span><div id=\"target-id69eb9d9959806\" class=\"collapseomatic_content \">\n<div class=\"thinktext\">No, there has not been a chemical reaction, because no new substances form &#8211; the only substance involved at any time is H<sub>2<\/sub>0.<\/div>\n<\/div>\n<div style=\"clear:both;line-height:16px;\">&nbsp;<\/div>\n<div style=\"max-width:750px;\">\n<div style=\"line-height:10px;\">\n<img decoding=\"async\" alt=\"\" src=\"\/\/www.chemicool.com\/ad.png\"\/>\n<\/div>\n<p><script async src=\"\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js\"><\/script><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-9461632227417539\" data-ad-slot=\"8753977201\" data-ad-format=\"auto\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>By Dr. Doug Stewart How important are chemical reactions? Long ago, people discovered that: substances can react to make new substances these reactions can be controlled The science of chemistry began when people began experimenting with chemical reactions systematically and organizing their results logically. As chemistry developed, scientists learned that living things exist only as [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"class_list":{"0":"post-4345","1":"page","2":"type-page","3":"status-publish","5":"entry"},"_links":{"self":[{"href":"https:\/\/www.chemicool.com\/elements\/wp-json\/wp\/v2\/pages\/4345","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.chemicool.com\/elements\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.chemicool.com\/elements\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.chemicool.com\/elements\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.chemicool.com\/elements\/wp-json\/wp\/v2\/comments?post=4345"}],"version-history":[{"count":14,"href":"https:\/\/www.chemicool.com\/elements\/wp-json\/wp\/v2\/pages\/4345\/revisions"}],"predecessor-version":[{"id":4388,"href":"https:\/\/www.chemicool.com\/elements\/wp-json\/wp\/v2\/pages\/4345\/revisions\/4388"}],"wp:attachment":[{"href":"https:\/\/www.chemicool.com\/elements\/wp-json\/wp\/v2\/media?parent=4345"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}