00:00:00.000 --> 00:00:03.280 Hello guys! I'm Professor Dave, let's talk about thermochemistry 00:00:09.720 --> 00:00:14.920 Thermochemistry is the branch of thermodynamics that deals with the heat absorbed or produced by one 00:00:14.920 --> 00:00:22.080 chemical reaction. a reaction may be, either exothermic, one that releases energy, or 00:00:22.080 --> 00:00:28.539 well endothermic, which absorbs energy. This change in energy is represented by Delta 00:00:28.539 --> 00:00:33.890 H, or what is the same, the change in the enthalpy of the reaction. For our purposes, we can think 00:00:33.890 --> 00:00:39.540 of the change in the enthalpy as if it were a change in the energy for the reaction, or 00:00:39.540 --> 00:00:44.760 the energy stored in all product links minus the energy stored in all 00:00:44.760 --> 00:00:50.469 the reagent bonds. If there is more energy in the products, Delta H 00:00:50.469 --> 00:00:54.590 it will be positive. This means that additional energy has to be provided, 00:00:54.590 --> 00:00:59.629 and it is, therefore, an endothermic reaction. If there is less energy in the products, 00:00:59.629 --> 00:01:06.000 it means that this extra energy has been released, and therefore it is an exothermic reaction. Energy 00:01:06.000 --> 00:01:10.610 which is the ability to do work, it can take many forms, like mechanics, 00:01:10.610 --> 00:01:15.509 electrical, chemical, heat, and so on. And, with a few exceptions to quantum mechanics, 00:01:15.509 --> 00:01:22.009 energy is conserved. This means that it can change in the form of, for example, the case of energy 00:01:22.009 --> 00:01:26.520 heat released when energy is released in a broken chemical bond, however 00:01:26.520 --> 00:01:31.640 it is not created or destroyed. The heat, represented by the letter q, is one 00:01:31.640 --> 00:01:36.549 more difficult thing to define, but a good way to say it is that the heat is the energy that 00:01:36.549 --> 00:01:41.600 it flows between a system and its surroundings due to a difference in 00:01:41.600 --> 00:01:46.930 temperature. Heat will always flow spontaneously from a high area 00:01:46.930 --> 00:01:52.450 temperature layer a low temperature zone. For a system, q will be 00:01:52.450 --> 00:01:57.950 positive if the heat is being absorbed by the system, and positive if the heat is 00:01:57.950 --> 00:02:02.780 released by the system. At constant temperature and pressure 00:02:02.780 --> 00:02:05.710 q = Delta H, 00:02:05.710 --> 00:02:10.950 the change of enthalpy. When we talk about thermochemistry we talk about energy 00:02:10.950 --> 00:02:12.080 in terms of 00:02:12.080 --> 00:02:17.830 joules or kilojoules. Another unit commonly used by chemists is calorie, which is equivalent 00:02:17.830 --> 00:02:23.510 at 4,184 joules. 1 calorie is the amount of energy needed 00:02:23.510 --> 00:02:29.910 to raise the temperature of one gram of water by one degree Celsius. This should not be 00:02:29.910 --> 00:02:34.860 to confuse with the calories of foods, which are calories with a capital C. These 00:02:34.860 --> 00:02:40.870 are actually kilocalories or 1000 calories, also abbreviated as kcal. 00:02:40.870 --> 00:02:45.210 There is a thermochemical equation that describes the change in enthalpy of one 00:02:45.210 --> 00:02:51.040 reaction in stoichiometric terms. In this, the Delta H that appears is specific to 00:02:51.040 --> 00:02:56.270 molar quantities given by the balanced equation, so if the number of moles of each 00:02:56.270 --> 00:03:02.760 substance, react in the manner indicated, we get a change in enthalpy as indicated. 00:03:02.760 --> 00:03:07.120 To find the enthalpy change for a specific amount of material you need to do a little 00:03:07.120 --> 00:03:13.020 stoichiometry. If they react twice as many moles of substance as listed, the 00:03:13.020 --> 00:03:17.340 Enthalpy change would also be twice what is mentioned. See if you understand! 00:03:49.020 --> 00:03:52.940 thanks for watching, guys. Subscribe to my channel for more tutorials and as always 00:03:52.950 --> 00:03:54.190 feel free to email me
Office location
Engineering company LOTUS®
Russia, Ekaterinburg, Lunacharskogo street, 240/12