{"id":8358,"date":"2013-10-29T21:23:54","date_gmt":"2013-10-29T21:23:54","guid":{"rendered":"http:\/\/www.mometrix.com\/academy\/?page_id=8358"},"modified":"2026-03-26T09:35:06","modified_gmt":"2026-03-26T14:35:06","slug":"laws-of-thermodynamics","status":"publish","type":"page","link":"https:\/\/www.mometrix.com\/academy\/laws-of-thermodynamics\/","title":{"rendered":"Laws of Thermodynamics"},"content":{"rendered":"\n\t\t\t<div id=\"mmDeferVideoEncompass_XNW0ZaJWeDI\" style=\"position: relative;\">\n\t\t\t<picture>\n\t\t\t\t<source srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.webp\" type=\"image\/webp\">\n\t\t\t\t<source srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.png\" type=\"image\/jpeg\"> \n\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" loading=\"eager\" id=\"videoThumbnailImage_XNW0ZaJWeDI\" data-source-videoID=\"XNW0ZaJWeDI\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.png\" alt=\"Laws of Thermodynamics Video\" height=\"464\" width=\"825\" class=\"size-full\" data-matomo-title = \"Laws of Thermodynamics\">\n\t\t\t<\/picture>\n\t\t\t<\/div>\n\t\t\t<style>img#videoThumbnailImage_XNW0ZaJWeDI:hover {cursor:pointer;} img#videoThumbnailImage_XNW0ZaJWeDI {background-size:contain;background-image:url(\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/07\/updated-laws-of-thermodynamics-64bee10be75d2.webp\");}<\/style>\n\t\t\t<script defer>\n\t\t\t  jQuery(\"img#videoThumbnailImage_XNW0ZaJWeDI\").click(function() {\n\t\t\t\tlet videoId = jQuery(this).attr(\"data-source-videoID\");\n\t\t\t\tlet helpTag = '<div id=\"mmDeferVideoYTMessage_XNW0ZaJWeDI\" style=\"display: none;position: absolute;top: -24px;width: 100%;text-align: center;\"><span style=\"font-style: italic;font-size: small;border-top: 1px solid #fc0;\">Having trouble? <a href=\"https:\/\/www.youtube.com\/watch?v='+videoId+'\" target=\"_blank\">Click here to watch on YouTube.<\/a><\/span><\/div>';\n\t\t\t\tlet tag = document.createElement(\"iframe\");\n\t\t\t\ttag.id = \"yt\" + videoId;\n\t\t\t\ttag.src = \"https:\/\/www.youtube-nocookie.com\/embed\/\" + videoId + \"?autoplay=1&controls=1&wmode=opaque&rel=0&egm=0&iv_load_policy=3&hd=0&enablejsapi=1\";\n\t\t\t\ttag.frameborder = 0;\n\t\t\t\ttag.allow = \"autoplay; fullscreen\";\n\t\t\t\ttag.width = this.width;\n\t\t\t\ttag.height = this.height;\n\t\t\t\ttag.setAttribute(\"data-matomo-title\",\"Laws of Thermodynamics\");\n\t\t\t\tjQuery(\"div#mmDeferVideoEncompass_XNW0ZaJWeDI\").html(tag);\n\t\t\t\tjQuery(\"div#mmDeferVideoEncompass_XNW0ZaJWeDI\").prepend(helpTag);\n\t\t\t\tsetTimeout(function(){jQuery(\"div#mmDeferVideoYTMessage_XNW0ZaJWeDI\").css(\"display\", \"block\");}, 2000);\n\t\t\t  });\n\t\t\t  \n\t\t\t<\/script>\n\t\t\n<p><script>\nfunction C4u_Function() {\n  var x = document.getElementById(\"C4u\");\n  if (x.style.display === \"none\") {\n    x.style.display = \"block\";\n  } else {\n    x.style.display = \"none\";\n  }\n}\n<\/script><\/p>\n<div class=\"moc-toc hide-on-desktop hide-on-tablet\">\n<div><button onclick=\"C4u_Function()\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2024\/12\/toc2.svg\" width=\"16\" height=\"16\" alt=\"show or hide table of contents\"><\/button><\/p>\n<p>On this page<\/p>\n<\/div>\n<nav id=\"C4u\" style=\"display:none;\">\n<ul>\n<li class=\"toc-h2\"><a href=\"#Zeroth_Law_of_Thermodynamics\" class=\"smooth-scroll\">Zeroth Law of Thermodynamics<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#First_Law_of_Thermodynamics\" class=\"smooth-scroll\">First Law of Thermodynamics<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Second_Law_of_Thermodynamics\" class=\"smooth-scroll\">Second Law of Thermodynamics<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Third_Law_of_Thermodynamics\" class=\"smooth-scroll\">Third Law of Thermodynamics<\/a><\/li>\n<\/ul>\n<\/nav>\n<\/div>\n<div class=\"accordion\"><input id=\"transcript\" type=\"checkbox\" class=\"spoiler_button\" \/><label for=\"transcript\">Transcript<\/label>\n<div class=\"spoiler\" id=\"transcript-spoiler\">\n<p>Hey, everyone! Welcome to this Mometrix video over the four laws of thermodynamics.<\/p>\n<p>Thermodynamics is a branch of physical science (or physics) that focuses on the correlation of heat and all other forms of energy, and, consequently, how all forms of energy relate to one another.<\/p>\n<p>Well, the four laws of thermodynamics work to define the foundational physical quantities that mark thermodynamic processes when at thermal equilibrium. These foundational physical quantities include temperature, energy, and entropy.<\/p>\n<p>Now, let\u2019s take a look at how these laws are defined.<\/p>\n<h2><span id=\"Zeroth_Law_of_Thermodynamics\" class=\"m-toc-anchor\"><\/span>Zeroth Law of Thermodynamics<\/h2>\n<p>\nThe zeroth law actually came after the first three laws of thermodynamics, but it was actually so fundamental and provided a basis for the other laws that it got the name <em>zeroth<\/em>. That way people knew the order in which they should learn or think through the laws.<\/p>\n<p>So, what does the zeroth law actually state? Let\u2019s take a look. Let\u2019s say that you have two systems, A and B, that are connected to each other with some sort of barrier between them. Well, the heat or energy of A will transfer over to B, or vise versa, the energy of B will transfer over to A. This is assuming that the wall is diathermic, meaning that heat can be exchanged, as opposed to an adiabatic wall which would not allow for heat to pass.<\/p>\n<p>Once heat or energy is transferred between two systems, such that there is no more heat being transferred (or the transference of heat stops), then the systems have reached equilibrium (more specifically thermal equilibrium since we are talking about heat). <\/p>\n<p>Now, let\u2019s say that we have another system, A and C, and they also reach equilibrium.<\/p>\n<p>Well, since A is in equilibrium with B, and A is in equilibrium with C, then when you take B and C and with them together with a diathermic wall, then there will be no transference of heat. This is because the two systems are already at equilibrium together.<\/p>\n<p>To say this mathematically: if \\(A = B\\) and \\(A=C\\), then \\(B=C\\).<\/p>\n<p>That is the zeroth law of thermodynamics. For some of you this may seem like common sense, to others it may seem counterintuitive, especially if you are super familiar with Boyle\u2019s law.<\/p>\n<p>Regardless, this what the zeroth law shows us, but it gives us much more than that. The illustration you just saw tells us something. What is that? What is that physical quantity which determines that the two systems will reach equilibrium, and the transference of heat will stop from one system to the other? Well, it\u2019s this very physical quantity that was discovered later. <\/p>\n<p>There were already two laws of thermodynamics in place, the first law and the second law. Well, in these two laws the term temperature was used, which was thought of as the degree of hotness, basically. While the term \u201ctemperature\u201d was being used in the first and second law, no one could actually define it. There wasn\u2019t really a way to define temperature within thermodynamics. So, the zeroth law was made, so that temperature could be defined. <\/p>\n<p>So, how is temperature defined?<\/p>\n<h3><span id=\"Temperature_Definition\" class=\"m-toc-anchor\"><\/span>Temperature Definition<\/h3>\n<p>\nIf there are two systems in contact with each other, then the direction of heat flow tells us that one body is at a higher temperature, and the receiving body is at a lower temperature. So, temperature is the physical quantity which determines the flow or direction of heat. So, temperature decides if heat will flow from A to B, or from B to A.<\/p>\n<p>Let\u2019s review that real quick. First, the zeroth law says this, \u201cIf two systems C and B are in thermal equilibrium separately with system A, then C and B are also in thermal equilibrium with each other.\u201d Secondly, the physical quantity defined in the zeroth law is temperature. And lastly, temperature can be defined as the physical quantity which determines the direction of flow of heat, and is the one that is equal in a state of equilibrium of two systems.<\/p>\n<p>Now let\u2019s take a look at the first law of thermodynamics.<\/p>\n<h2><span id=\"First_Law_of_Thermodynamics\" class=\"m-toc-anchor\"><\/span>First Law of Thermodynamics<\/h2>\n<p>\nHere is what the first law of thermodynamics states: heat energy given to a system is converted to its internal energy and work done on that system.<\/p>\n<p>To put this even simpler, the first law of thermodynamics just states that energy cannot be created or destroyed, it can only be transformed.<\/p>\n<h3><span id=\"First_Law_of_Thermodynamics_Equation\" class=\"m-toc-anchor\"><\/span>First Law of Thermodynamics Equation<\/h3>\n<p>\nLet\u2019s look at that mathematically. Internal energy, represented by \\(\u0394U\\), is equal to heat energy plus work done.<\/p>\n<div class=\"examplesentence\">\\(\u0394U = q + w\\)<\/div>\n<p>\n&nbsp;<br \/>\nThis equation is known as the first law of thermodynamics. But, I\u2019m guessing this still doesn\u2019t make sense to you. I don\u2019t blame you.<\/p>\n<p>Let\u2019s look at it this way. You have a system. Everything on the outside of the system is the surroundings. Well, energy can flow either into the system, or out of the system. There are two ways in which energy can flow in and out of a system, which is through heat and work. <\/p>\n<p>So, let\u2019s say that heat flows into the system. When heat flows into the system, then the system accumulates or gains energy. That energy is called the internal energy of the system, which is where we get our symbol U. The surroundings can do work on the system.<\/p>\n<p>So, heat and work are the two ways in which a system can increase its internal energy. If the system\u2019s surroundings were to do 150 J of work on the system, that means that the system&#8217;s internal energy increases by 150 J, and since the change is positive, \\(\u0394U\\) goes up.<\/p>\n<p>And, since we know that energy cannot be created or destroyed (only transferred), the energy had to come from somewhere\u2014the surroundings. So, if the system&#8217;s internal energy increases, then the energy of the surroundings must decrease.<\/p>\n<p>Another way to think through this might be to think through the old \u201cif you have 5 quarters and take 1 away\u201d example. Let\u2019s say you were selling a sticker for $1.25, and that someone is looking to buy the sticker. Well, when someone does buy the sticker, the amount of money that you have will increase by $1.25, but the amount of money that the other person has will decrease by $1.25. The money doesn\u2019t just come from thin air, it\u2019s coming from somewhere, or someone in this case.<\/p>\n<p>In order for the amount of money that you have to increase, someone else\u2019s money has to decrease. Now, sure, in the case of money, the government could create more, but that doesn\u2019t really apply on a day-to-day basis when it comes to buying and spending.<\/p>\n<p>Well, energy follows this same principle. It cannot be created or destroyed, it\u2019s simply transformed or transferred from one place to another.<\/p>\n<h2><span id=\"Second_Law_of_Thermodynamics\" class=\"m-toc-anchor\"><\/span>Second Law of Thermodynamics<\/h2>\n<p>\nNow, the second law of thermodynamics might seem like an odd law. Why? Well, firstly because the second law of thermodynamics doesn\u2019t tell us what can happen or what is possible, it only tells us what cannot be done or what is not possible. Another reason it might seem odd is because there are several ways to state it!<\/p>\n<p>The second law of Thermodynamics states that the efficiency of a process can never be one, or 100% of any machine. If a machine or process operated with 100% efficiency, then all of the heat or energy put into a system would be completely converted into work done, and there would be no heat rejected out. The Second Law tells us that this is NOT the case. The second thing that the second law of thermodynamics states is that unless you apply a pump to a system, there is no way to send heat from a cooler source to a source at a higher temperature.<\/p>\n<p>Another popular way to state this law, as put by Clausius, is, \u201cNo process is possible whose sole result is the transfer of heat from a colder object to a hotter object.\u201d<\/p>\n<p>Put very simply, the second law of thermodynamics tells us that heat will never flow from a colder object to a hotter object, unless you use a pump to do so. Like how a pump is used to cool the inside of a refrigerator. In every other case, however, heat always goes from the object at a higher temperature to the object with the lower temperature. And, the other thing it states is that within a system or machine, heat or energy will never be 100% converted into work done. So, if I put 100 J into a system, and I get more than 100 J out of the system, then one of three things happen:<\/p>\n<ol style=\"line-height:30px\">\n<li>I lied.<\/li>\n<li>I miscalculated either my input or output.<\/li>\n<li>Or three, I just turned all of physics and science on its head and defied all of it.<\/li>\n<\/ol>\n<h2><span id=\"Third_Law_of_Thermodynamics\" class=\"m-toc-anchor\"><\/span>Third Law of Thermodynamics<\/h2>\n<p>\nThe third and last law of thermodynamics defines absolute zero and brings together the concepts of entropy and temperature from the latter laws.<\/p>\n<p>The third law states that the entropy of a perfect crystal approaches zero at a temperature of absolute zero. We can\u2019t actually achieve absolute zero experimentally, or at least you probably won\u2019t. This is because we know from the second law that heat is spontaneously moving from a warmer body to a cooler body. So, the object that you are trying to get to absolute zero will be constantly taking in heat from its surroundings. <\/p>\n<p>I said that the lowest possible entropy will only occur in a perfect crystal, well a perfect crystal is a structure where all of the atoms are identical and are positioned in perfectly symmetrical ways. If there are any imperfections in the crystal, then that imperfection carries an energy with it, which does not allow for the minimization of entropy. <\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2025\/01\/crystal-molecules.webp\" alt=\"\" width=\"\" height=\"\" class=\"aligncenter size-full wp-image-215971\"  role=\"img\" style=\"box-shadow: 1.5px 1.5px 3px gray;\"  \/><\/p>\n<p>Another important note is that if we can\u2019t get to perfect zero, then there will never be complete stillness in our universe, because we will always have some sort of motion due to thermal energy.<\/p>\n<p>I hope that this video over the four laws of thermodynamics was helpful to you.<\/p>\n<p>See you guys next time!<\/p>\n<\/div>\n<\/div>\n\n<div class=\"home-buttons\">\n<p><a href=\"https:\/\/www.mometrix.com\/academy\/chemistry\/\">Return to Chemistry Videos<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Return to Chemistry Videos<\/p>\n","protected":false},"author":1,"featured_media":186200,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"open","template":"","meta":{"footnotes":""},"class_list":{"0":"post-8358","1":"page","2":"type-page","3":"status-publish","4":"has-post-thumbnail","6":"page_category-chemistry-thermodynamics","7":"page_type-video","8":"subject_matter-science"},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/8358","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/comments?post=8358"}],"version-history":[{"count":7,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/8358\/revisions"}],"predecessor-version":[{"id":279613,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/8358\/revisions\/279613"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/media\/186200"}],"wp:attachment":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/media?parent=8358"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}