**SECTION II FUNDAMENTALS OF MOLECULAR PHYSICS AND THERMODYNAMICS**

*Lecture 10. Basic concepts and definitions. Internal energy of the system. Internal energy of an ideal gas. Work and heat as forms of energy transfer. Heat capacity. Specific heat. Heat balance equation. First law of thermodynamics. adiabatic process. The principle of operation of a heat engine. heat engine efficiency. The second law of thermodynamics. Thermodynamic temperature scale. Refrigeration machines. Thermal engines. Protection of Nature.*

**1.** What is the difference between the internal energy of an ideal gas and the internal energy of a liquid or solid substance?

1. Determine the internal energy of 2 moles of helium at a temperature of 27 °C

2. Determine the internal energy of helium filling a balloon with a volume of 80 m ^{3} , at a pressure of 100 kPa, a helium temperature of 273 K.

3. The volume of a gas expanding at a constant pressure of 100 kPa has increased by 2 liters. Determine the work done by the gas in this process.

4. What work was done during isobaric compression of 6 moles of hydrogen if its temperature changed by 50 K?

5. During isobaric heating of a certain amount of ideal gas from 17 to 117 ° C, the gas did work of 4 kJ. Find the amount of gas substance.

6. During the isobaric expansion of an ideal monatomic gas, 200 J work was done. Determine the change in the internal energy of the gas.

7. Determine the mass of hydrogen under the piston in a cylindrical vessel, if when it was heated from 250 to 680 K at constant pressure, work was done 392 J. The molar mass of hydrogen is 0.002 kg / mol.

8. What work does the gas do during the transition from state 1 to state 3?

9. What work did a monatomic gas do in the process depicted in the p V-diagram /

10. An ideal gas received an amount of heat equal to 300 J and did work equal to 100 J. How did the internal energy of the gas change in this case?

11. What is the change in the internal energy of the gas if the amount of heat of 300 J is transferred to it, and the external forces do 500 J of work on it?

12. When transferring 300 J of heat to the gas, its internal energy decreased by 100 J. What work did the gas do?

13. An ideal gas gave off an amount of heat of 600 J, while its internal energy increased by 200 J. What is the work done on the gas?

14. An ideal gas received an amount of heat of 100 J, and at the same time, the internal energy of the gas decreased by 100 J. What is the work done by external forces on the gas?

15. The pressure of an ideal monatomic gas has decreased by 50 kPa. Gas is in a closed vessel at a constant volume of 0.3 m ^{3} . How much heat was given off by the gas?

16. A monatomic ideal gas, initially occupying a volume of 5 m ^{3} , is isochorically transferred to a state in which its pressure increased by 400 kPa. How much heat was imparted to the gas?

17. The efficiency of an ideal heat engine is 40%. During the cycle, it receives from the heater an amount of heat of 1200 J. What useful work does it do in this case?

18. The heat engine has an efficiency of 40%. For one cycle of work, it gives the refrigerator an amount of heat of 600 J. How much heat does the machine receive from the heater?

19. Efficiency of an ideal heat engine operating on the Carnot cycle, 40%. What useful work does this machine do per cycle if it gives the refrigerator an amount of heat of 300 J?

20. Calculate the maximum efficiency of the heat engine if the heater temperature is 127 °C and the refrigerator temperature is 27 °C.

21. The temperature of the heater of an ideal heat engine is 527 ° C, and the temperature of the refrigerator is 127 ° C. Determine the amount of heat received by the machine from the heater if it did 700 J of work.

**Homework:** Myakishev G.Ya., Bukhovtsev, N.N. Physics Grade 10 **Chapter 13 Tasks** Preparation of essays on the topics: “History of the development of a heat engine”, “Diesel engine,” Internal combustion engine, “Jet engine,” Steam turbine “,” Gas turbine “,” Jet engines and the basics of the operation of a heat engine ” , “Environmental problems and possible solutions”, “Ecological problems associated with the use of heat engines”

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