1. First Law of Thermodynamics

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