{"id":319,"date":"2024-04-02T07:17:23","date_gmt":"2024-04-02T06:17:23","guid":{"rendered":"https:\/\/tutors4you.com\/?page_id=319"},"modified":"2024-04-02T07:17:23","modified_gmt":"2024-04-02T06:17:23","slug":"first-law-of-thermodynamics","status":"publish","type":"page","link":"https:\/\/tutors4you.com\/index.php\/first-law-of-thermodynamics\/","title":{"rendered":"First Law of Thermodynamics"},"content":{"rendered":"\n
\n\t\t\t\n\t\t\t

Let us consider one of the most fundamental\n principles of the physical world – The Law of\n Conservation of Energy – It states that <\/font>energy cannot be\n created or destroyed.<\/font><\/p>\n

Now, let us apply this law to various\n processes in chemistry. It can be written as <\/font><\/p>\n

U\n = Q + W<\/font><\/p>\n

Where U is the change in internal energy<\/font><\/p>\n

           \n Q is heat<\/font><\/p>\n

           \n W is work<\/font><\/p>\n

According to this, there are two kinds of\n processes that can lead to a change in the internal\n energy of the system – they are heat and work.<\/font><\/p>\n

Let us consider the sign convention:<\/font><\/p>\n

(i)    Heat flowing into the\n system is positive. It increases the internal energy of\n the system.<\/font><\/p>\n

(ii)   Heat flowing out of the\n system is negative. It decreases the internal energy of\n the system.<\/font><\/p>\n

(iii)  Work done by the system is\n positive. It decreases the internal energy of the system.<\/font><\/p>\n

Note that: U is a state function. From a\n given value of ?U, one cannot make out whether this\n change has come about by adding heat to it or by doing\n work on it.<\/font><\/p>\n

System work:  <\/font>When we talk about\n work done by a thermodynamic system, we are usually\n talking about the work done by a gas in expanding.<\/font><\/p>\n

(i)    Work done at constant\n pressure<\/font><\/p>\n

W = PV<\/font><\/p>\n

It is given by the area under the PV graph<\/font><\/p>\n

(ii)    Work done when the\n pressure is changing<\/font><\/p>\n

W = PdV<\/font><\/p>\n

Note: That work and heat are not state\n functions. They do depend on the path followed between\n the initial and final states.<\/font><\/p>\n

Example<\/font><\/p>\n

Calculate the internal energy change in each\n of the following cases:<\/font><\/p>\n

(i)    A system absorbs 5kJ\n of heat and does 1kJ of work.<\/font><\/p>\n

(ii)   5kJ of work is done on the\n system and 1kJ of heat is given out by the system.<\/font><\/p>\n

(i)    Q = +5kJ<\/font><\/p>\n

       W =\n -1kJ<\/font><\/p>\n

       U = Q + W = 5 +\n (-1) = 4kJ<\/font><\/p>\n

(ii)   W = +5kJ<\/font><\/p>\n

       Q =\n -1kJ<\/font><\/p>\n

       U = Q + W = -1 + 5\n = 4kJ<\/font><\/p>\n

       In both\n the cases, the interval energy of the system increases.<\/font><\/p>\n

   <\/b><\/font><\/p>\n \t\t\n \n\t\t<\/div>\n","protected":false},"excerpt":{"rendered":"

Let us consider one of the most fundamental principles of the physical world – The Law of Conservation of Energy – It states that energy cannot be created or destroyed. Now, let us apply this law to various processes in chemistry. It can be written as U = Q + W Where U is the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-319","page","type-page","status-publish","hentry"],"blocksy_meta":[],"yoast_head":"\nFirst Law of Thermodynamics - Tutors 4 You<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/tutors4you.com\/index.php\/first-law-of-thermodynamics\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"First Law of Thermodynamics - Tutors 4 You\" \/>\n<meta property=\"og:description\" content=\"Let us consider one of the most fundamental principles of the physical world – The Law of Conservation of Energy – It states that energy cannot be created or destroyed. 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