1. First Law of Thermodynamics Conservation of Energy for Thermal Systems

2. Joule Equivalent of Heat James Joule showed that mechanical energy could be converted to heat and arrived at the conclusion that heat was another form of energy. He showed that 1 calorie of heat was equivalent to 4.184 J of work. 1 cal = 4.184 J

3. Energy Mechanical Energy: KE, PE, E Work is done by energy transfer. Heat is another form of energy. Need to expand the conservation of energy principle to accommodate thermal systems.

4. First Law of Thermodynamics The internal energy of a system changes due to work and heat: Heat is positive when the system gains heat. Work is positive when work is done by the system.

5. 1 st Law of Thermodynamics What happens to the gas if the piston is moved inwards?

6. 1 st Law of Thermodynamics If the container is insulated the temperature will rise, the atoms move faster and the pressure rises. Is there more internal energy in the gas?

7. 1 st Law of Thermodynamics External agent did work in pushing the piston inward. W = Fd =(PA)  x W =P  V xx

8. 1 st Law of Thermodynamics Work done on the gas equals the change in the gases internal energy, W =  U xx

9. 1 st Law of TD Let’s change the situation: Keep the piston fixed at its original location. Place the cylinder on a hot plate. What happens to gas?

10. Heat flows into the gas. Atoms move faster, internal energy increases. Q = heat in Joules  U = change in internal energy in Joules. Q =  U

11. 1 st Law of TD What if we added heat and pushed the piston in at the same time? F

12. 1 st Law of TD Work is done on the gas, heat is added to the gas and the internal energy of the gas increases! Q = W +  U F

13. 2 nd Law of Thermodynamics: Law of Entropy Heat flows spontaneously from a substance at higher temperature to a substance at lower temperature. Entropy (chaos) – everything in the universe always moves from an ordered state to a more disordered state. Randomness is always increasing.

14. Entropy A measure of molecular disorder: The arrow of time: disorder of universe always increases with time. Perpetual motion machines are impossible. A thermodynamic limit to the efficiency of engines.