Thermodynamics

1. Thermodynamics Thermodynamic Processes

2. The First Law of Thermodynamics • The First Law of Thermodynamics – conservation of a system’s internal energy, work, and heat • In any process, the total energy of the universe remains constant • For a thermodynamic cycle the sum of net heat supplied to the system and the net work done by the system is equal to zero

3. The First Law of Thermodynamics • The first law of thermodynamics can be expressed mathematically • Change in systems internal energy = the energy transferred to or from system as heat – energy transferred to or from the system as work • ΔU = Q – W

4. The First Law of Thermodynamics • All terms should have the same units, usually joules (J) • Q is positive for energy added to the system • Negative for energy released from the system • W is positive for work done by the system • Negative for work done on the system

5. Signs of Q and W for a System

6. The First Law of Thermodynamics for Special Processes

7. Cyclic Processes • The change in internal energy of a system is zero in a cyclic process • So ΔUnet = 0 and Qnet = Wnet • Cyclic process – a thermodynamic process in which a system returns to the same conditions under which it started

8. Cyclic Processes • Refrigerators use mechanical work to create a temperature difference and therefore transfer energy • Heat engines use heat to do work • Hot gases pushing against a piston in an internal combustion engine

9. Cyclic Processes

10. Cyclic Processes

11. Cyclic Processes

12. Cyclic Processes