13. The internal energy of heat is 1. Preliminary knowledge of molecular theory: matter is composed of a large number of molecules, which are constantly moving irregularly, and there are repulsion and attraction between molecules. 2. Diffusion: When two different substances contact each other, the phenomenon that they enter each other is called diffusion, and the essence of diffusion is caused by the random movement of molecules. The higher the temperature, the faster the diffusion, that is, the more intense the random movement of molecules. 3. Heat: the energy transferred in the process of heat transfer. The unit of heat is cola (ear). 4. Specific heat (capacity): When the temperature of a substance per unit mass increases or decreases by 65438 0℃, the heat absorbed or released is called specific heat. The unit of specific heat is coke/(kg℃). Calculation of heat absorbed or released by a substance: Q = cm △ t The specific heat of water is 4.2×103j/(kg℃). The relatively large specific heat of water can be used to explain the phenomenon that water is used as a coolant to protect seedlings in winter and the temperature difference in inland areas is large. 5. Combustion value of fuel: 1kg heat released by complete combustion of a certain substance, and the unit of combustion value is coke/kg. Calculation of heat released by fuel combustion: Q = QM ① Reasons why liquid hydrogen has a high calorific value and is used as rocket fuel ② Ways to save fuel: A. Improve combustion conditions, make fuel burn fully and reduce heat loss 6. Internal energy: the sum of kinetic energy and molecular potential energy of irregular motion of a large number of molecules in an object Understanding: ① The kinetic energy possessed by the random motion of a single molecule is not called internal energy; The kinetic energy of a large number of molecules moving regularly is not called internal energy. Internal energy is another form of energy different from mechanical energy. ② The internal energy of the same object can be reflected from its temperature. When the temperature is high, it has more internal energy, and when the temperature is low, it has less internal energy. However, the temperature of different objects does not directly indicate the amount of internal energy (for example, the internal energy of a glass of water at 5℃ and that of a drop of water at 10℃), so heat is transferred from a high-temperature object to a low-temperature object, not from an object with more internal energy to an object with less internal energy. ③ There are two ways to change internal energy: doing work and heat transfer. The essence of work changing internal energy is the mutual transformation between internal energy and other forms of energy, while the essence of heat transfer changing internal energy is the transfer of internal energy. But they are equivalent in changing internal energy. 7. Heat engine: a machine that uses internal energy to do work. A heat engine converts internal energy into mechanical energy. Including internal combustion engines, rockets and so on. 8. Heat engine efficiency: the ratio of the energy used to do work to the energy released by the complete combustion of fuel. 9. Law of energy transformation and conservation: energy will neither disappear nor be created, it can only be transformed from one form to another, or transferred from one object to another. In the process of transformation and transfer, the total amount of energy remains unchanged.