{"id":287,"date":"2017-10-26T19:55:57","date_gmt":"2017-10-26T19:55:57","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/chapter\/heat\/"},"modified":"2019-01-28T18:11:40","modified_gmt":"2019-01-28T18:11:40","slug":"heat","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/chapter\/heat\/","title":{"raw":"Module 5 Heat","rendered":"Module 5 Heat"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Define heat as transfer of energy.<\/li>\r\n<\/ul>\r\n<\/div>\r\nIn the chapter Work, Energy, and Energy Resources, we defined work as force times distance and learned that work done on an object changes its kinetic energy. We also saw in <a href=\".\/part\/7540-2\/\" target=\"_blank\" rel=\"noopener\">Temperature, Kinetic Theory, and the Gas Laws<\/a> that temperature is proportional to the (average) kinetic energy of atoms and molecules. We say that a thermal system has a certain internal energy: its internal energy is higher if the temperature is higher. If two objects at different temperatures are brought in contact with each other, energy is transferred from the hotter to the colder object until equilibrium is reached and the bodies reach thermal equilibrium (i.e., they are at the same temperature). No work is done by either object, because no force acts through a distance. The transfer of energy is caused by the temperature difference, and ceases once the temperatures are equal. These observations lead to the following definition of <em>heat<\/em>: Heat is the spontaneous transfer of energy due to a temperature difference.\r\n\r\nAs noted in the chapter Temperature, Kinetic Theory, and the Gas Laws, heat is often confused with temperature. For example, we may say the heat was unbearable, when we actually mean that the temperature was high. Heat is a form of energy, whereas temperature is not. The misconception arises because we are sensitive to the flow of heat, rather than the temperature.\r\n\r\nOwing to the fact that heat is a form of energy, it has the SI unit of <em>joule<\/em> (J). The <em>calorie<\/em> (cal) is a common unit of energy, defined as the energy needed to change the temperature of 1.00 g of water by 1.00\u00baC\u2014specifically, between 14.5\u00baC and 15.5\u00baC, since there is a slight temperature dependence. Perhaps the most common unit of heat is the <em>kilocalorie<\/em> (kcal), which is the energy needed to change the temperature of 1.00 kg of water by 1.00\u00baC. Since mass is most often specified in kilograms, kilocalorie is commonly used. Food calories (given the notation Cal, and sometimes called \u201cbig calorie\u201d) are actually kilocalories (1 kilocalorie = 1000 calories), a fact not easily determined from package labeling.\r\n\r\n[caption id=\"attachment_12241\" align=\"aligncenter\" width=\"875\"]<img class=\"size-full wp-image-12241\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2548\/2017\/10\/26195554\/Figure_15_01_01a.jpg\" alt=\"In figure a there is a soft drink can and an ice cube placed on a surface at a distance from each other. The temperatures of the can and the ice cube are T one and T two, respectively, where T one is not equal to T two. In figure b, the soft drink can and the ice cube are placed in contact on the surface. The temperature of both is T prime.\" width=\"875\" height=\"854\" \/> Figure 1. In figure (a) the soft drink and the ice have different temperatures, T<sub>1<\/sub> and T<sub>2<\/sub>, and are not in thermal equilibrium. In figure (b), when the soft drink and ice are allowed to interact, energy is transferred until they reach the same temperature T\u2032, achieving equilibrium. Heat transfer occurs due to the difference in temperatures. In fact, since the soft drink and ice are both in contact with the surrounding air and bench, the equilibrium temperature will be the same for both.[\/caption]\r\n<h2>Mechanical Equivalent of Heat<\/h2>\r\nIt is also possible to change the temperature of a substance by doing work. Work can transfer energy into or out of a system. This realization helped establish the fact that heat is a form of energy. James Prescott Joule (1818\u20131889) performed many experiments to establish the <em>mechanical equivalent of heat\u2014the work needed to produce the same effects as heat transfer<\/em>. In terms of the units used for these two terms, the best modern value for this equivalence is 1.000 kcal = 4186 J.\r\n\r\nWe consider this equation as the conversion between two different units of energy.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"450\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2548\/2017\/10\/26195556\/Figure_15_01_02a.jpg\" alt=\"In the figure, there is a can of known volume full of water and fitted with a thermometer at the top. On both sides of the can two blocks of weight W each hang from cords. The cords pass over two pulleys and wind around a cylindrical roller. There is a handle attached with the roller to rotate it manually. Submerged in the water are some paddles attached to a vertical rod attached at the bottom of the roller. When the lever is rotated, the paddles move inside the water.\" width=\"450\" height=\"401\" \/> Figure 2. Schematic depiction of Joule\u2019s experiment that established the equivalence of heat and work.[\/caption]\r\n\r\nFigure 2\u00a0above shows one of Joule\u2019s most famous experimental setups for demonstrating the mechanical equivalent of heat. It demonstrated that work and heat can produce the same effects, and helped establish the principle of conservation of energy. Gravitational potential energy (PE) (work done by the gravitational force) is converted into kinetic energy (KE), and then randomized by viscosity and turbulence into increased average kinetic energy of atoms and molecules in the system, producing a temperature increase. His contributions to the field of thermodynamics were so significant that the SI unit of energy was named after him.\r\n\r\nHeat added or removed from a system changes its internal energy and thus its temperature. Such a temperature increase is observed while cooking. However, adding heat does not necessarily increase the temperature. An example is melting of ice; that is, when a substance changes from one phase to another. Work done on the system or by the system can also change the internal energy of the system. Joule demonstrated that the temperature of a system can be increased by stirring. If an ice cube is rubbed against a rough surface, work is done by the frictional force. A system has a well-defined internal energy, but we cannot say that it has a certain \u201cheat content\u201d or \u201cwork content.\u201d We use the phrase \u201cheat transfer\u201d to emphasize its nature.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Check Your Understanding<\/h3>\r\nTwo samples (A and B) of the same substance are kept in a lab. Someone adds 10 kilojoules (kJ) of heat to one sample, while 10 kJ of work is done on the other sample. How can you tell to which sample the heat was added?\r\n<h4>Solution<\/h4>\r\nHeat and work both change the internal energy of the substance. However, the properties of the sample only depend on the internal energy so that it is impossible to tell whether heat was added to sample A or B.\r\n\r\n<\/div>\r\n<h2>Section Summary<\/h2>\r\n<ul>\r\n \t<li>Heat and work are the two distinct methods of energy transfer.<\/li>\r\n \t<li>Heat is energy transferred solely due to a temperature difference.<\/li>\r\n \t<li>Any energy unit can be used for heat transfer, and the most common are kilocalorie (kcal) and joule (J).<\/li>\r\n \t<li>Kilocalorie is defined to be the energy needed to change the temperature of 1.00 kg of water between 14.5\u00baC and 15.5\u00baC.<\/li>\r\n \t<li>The mechanical equivalent of this heat transfer is 1.00 kcal=4186 J.<\/li>\r\n<\/ul>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Conceptual Questions<\/h3>\r\n<ol>\r\n \t<li>How is heat transfer related to temperature?<\/li>\r\n \t<li>Describe a situation in which heat transfer occurs. What are the resulting forms of energy?<\/li>\r\n \t<li>When heat transfers into a system, is the energy stored as heat? Explain briefly.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<h2>\u00a0Glossary<\/h2>\r\n<strong>heat:<\/strong>\u00a0the spontaneous transfer of energy due to a temperature difference\r\n\r\n<strong>kilocalorie:<\/strong>\u00a01 kilocalorie = 1000 calories\r\n\r\n<strong>mechanical equivalent of heat:<\/strong>\u00a0the work needed to produce the same effects as heat transfer","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Define heat as transfer of energy.<\/li>\n<\/ul>\n<\/div>\n<p>In the chapter Work, Energy, and Energy Resources, we defined work as force times distance and learned that work done on an object changes its kinetic energy. We also saw in <a href=\".\/part\/7540-2\/\" target=\"_blank\" rel=\"noopener\">Temperature, Kinetic Theory, and the Gas Laws<\/a> that temperature is proportional to the (average) kinetic energy of atoms and molecules. We say that a thermal system has a certain internal energy: its internal energy is higher if the temperature is higher. If two objects at different temperatures are brought in contact with each other, energy is transferred from the hotter to the colder object until equilibrium is reached and the bodies reach thermal equilibrium (i.e., they are at the same temperature). No work is done by either object, because no force acts through a distance. The transfer of energy is caused by the temperature difference, and ceases once the temperatures are equal. These observations lead to the following definition of <em>heat<\/em>: Heat is the spontaneous transfer of energy due to a temperature difference.<\/p>\n<p>As noted in the chapter Temperature, Kinetic Theory, and the Gas Laws, heat is often confused with temperature. For example, we may say the heat was unbearable, when we actually mean that the temperature was high. Heat is a form of energy, whereas temperature is not. The misconception arises because we are sensitive to the flow of heat, rather than the temperature.<\/p>\n<p>Owing to the fact that heat is a form of energy, it has the SI unit of <em>joule<\/em> (J). The <em>calorie<\/em> (cal) is a common unit of energy, defined as the energy needed to change the temperature of 1.00 g of water by 1.00\u00baC\u2014specifically, between 14.5\u00baC and 15.5\u00baC, since there is a slight temperature dependence. Perhaps the most common unit of heat is the <em>kilocalorie<\/em> (kcal), which is the energy needed to change the temperature of 1.00 kg of water by 1.00\u00baC. Since mass is most often specified in kilograms, kilocalorie is commonly used. Food calories (given the notation Cal, and sometimes called \u201cbig calorie\u201d) are actually kilocalories (1 kilocalorie = 1000 calories), a fact not easily determined from package labeling.<\/p>\n<div id=\"attachment_12241\" style=\"width: 885px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-12241\" class=\"size-full wp-image-12241\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2548\/2017\/10\/26195554\/Figure_15_01_01a.jpg\" alt=\"In figure a there is a soft drink can and an ice cube placed on a surface at a distance from each other. The temperatures of the can and the ice cube are T one and T two, respectively, where T one is not equal to T two. In figure b, the soft drink can and the ice cube are placed in contact on the surface. The temperature of both is T prime.\" width=\"875\" height=\"854\" \/><\/p>\n<p id=\"caption-attachment-12241\" class=\"wp-caption-text\">Figure 1. In figure (a) the soft drink and the ice have different temperatures, T<sub>1<\/sub> and T<sub>2<\/sub>, and are not in thermal equilibrium. In figure (b), when the soft drink and ice are allowed to interact, energy is transferred until they reach the same temperature T\u2032, achieving equilibrium. Heat transfer occurs due to the difference in temperatures. In fact, since the soft drink and ice are both in contact with the surrounding air and bench, the equilibrium temperature will be the same for both.<\/p>\n<\/div>\n<h2>Mechanical Equivalent of Heat<\/h2>\n<p>It is also possible to change the temperature of a substance by doing work. Work can transfer energy into or out of a system. This realization helped establish the fact that heat is a form of energy. James Prescott Joule (1818\u20131889) performed many experiments to establish the <em>mechanical equivalent of heat\u2014the work needed to produce the same effects as heat transfer<\/em>. In terms of the units used for these two terms, the best modern value for this equivalence is 1.000 kcal = 4186 J.<\/p>\n<p>We consider this equation as the conversion between two different units of energy.<\/p>\n<div style=\"width: 460px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2548\/2017\/10\/26195556\/Figure_15_01_02a.jpg\" alt=\"In the figure, there is a can of known volume full of water and fitted with a thermometer at the top. On both sides of the can two blocks of weight W each hang from cords. The cords pass over two pulleys and wind around a cylindrical roller. There is a handle attached with the roller to rotate it manually. Submerged in the water are some paddles attached to a vertical rod attached at the bottom of the roller. When the lever is rotated, the paddles move inside the water.\" width=\"450\" height=\"401\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 2. Schematic depiction of Joule\u2019s experiment that established the equivalence of heat and work.<\/p>\n<\/div>\n<p>Figure 2\u00a0above shows one of Joule\u2019s most famous experimental setups for demonstrating the mechanical equivalent of heat. It demonstrated that work and heat can produce the same effects, and helped establish the principle of conservation of energy. Gravitational potential energy (PE) (work done by the gravitational force) is converted into kinetic energy (KE), and then randomized by viscosity and turbulence into increased average kinetic energy of atoms and molecules in the system, producing a temperature increase. His contributions to the field of thermodynamics were so significant that the SI unit of energy was named after him.<\/p>\n<p>Heat added or removed from a system changes its internal energy and thus its temperature. Such a temperature increase is observed while cooking. However, adding heat does not necessarily increase the temperature. An example is melting of ice; that is, when a substance changes from one phase to another. Work done on the system or by the system can also change the internal energy of the system. Joule demonstrated that the temperature of a system can be increased by stirring. If an ice cube is rubbed against a rough surface, work is done by the frictional force. A system has a well-defined internal energy, but we cannot say that it has a certain \u201cheat content\u201d or \u201cwork content.\u201d We use the phrase \u201cheat transfer\u201d to emphasize its nature.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>Check Your Understanding<\/h3>\n<p>Two samples (A and B) of the same substance are kept in a lab. Someone adds 10 kilojoules (kJ) of heat to one sample, while 10 kJ of work is done on the other sample. How can you tell to which sample the heat was added?<\/p>\n<h4>Solution<\/h4>\n<p>Heat and work both change the internal energy of the substance. However, the properties of the sample only depend on the internal energy so that it is impossible to tell whether heat was added to sample A or B.<\/p>\n<\/div>\n<h2>Section Summary<\/h2>\n<ul>\n<li>Heat and work are the two distinct methods of energy transfer.<\/li>\n<li>Heat is energy transferred solely due to a temperature difference.<\/li>\n<li>Any energy unit can be used for heat transfer, and the most common are kilocalorie (kcal) and joule (J).<\/li>\n<li>Kilocalorie is defined to be the energy needed to change the temperature of 1.00 kg of water between 14.5\u00baC and 15.5\u00baC.<\/li>\n<li>The mechanical equivalent of this heat transfer is 1.00 kcal=4186 J.<\/li>\n<\/ul>\n<div class=\"textbox key-takeaways\">\n<h3>Conceptual Questions<\/h3>\n<ol>\n<li>How is heat transfer related to temperature?<\/li>\n<li>Describe a situation in which heat transfer occurs. What are the resulting forms of energy?<\/li>\n<li>When heat transfers into a system, is the energy stored as heat? Explain briefly.<\/li>\n<\/ol>\n<\/div>\n<h2>\u00a0Glossary<\/h2>\n<p><strong>heat:<\/strong>\u00a0the spontaneous transfer of energy due to a temperature difference<\/p>\n<p><strong>kilocalorie:<\/strong>\u00a01 kilocalorie = 1000 calories<\/p>\n<p><strong>mechanical equivalent of heat:<\/strong>\u00a0the work needed to produce the same effects as heat transfer<\/p>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-287\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>College Physics. <strong>Authored by<\/strong>: OpenStax College. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/031da8d3-b525-429c-80cf-6c8ed997733a\/College_Physics\">http:\/\/cnx.org\/contents\/031da8d3-b525-429c-80cf-6c8ed997733a\/College_Physics<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Located at License<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":3,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"College Physics\",\"author\":\"OpenStax College\",\"organization\":\"\",\"url\":\"http:\/\/cnx.org\/contents\/031da8d3-b525-429c-80cf-6c8ed997733a\/College_Physics\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Located at License\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-287","chapter","type-chapter","status-publish","hentry"],"part":1073,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/pressbooks\/v2\/chapters\/287","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":1,"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/pressbooks\/v2\/chapters\/287\/revisions"}],"predecessor-version":[{"id":1215,"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/pressbooks\/v2\/chapters\/287\/revisions\/1215"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/pressbooks\/v2\/parts\/1073"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/pressbooks\/v2\/chapters\/287\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/wp\/v2\/media?parent=287"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/pressbooks\/v2\/chapter-type?post=287"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/wp\/v2\/contributor?post=287"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/ivytech-sci111\/wp-json\/wp\/v2\/license?post=287"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}