1. Chapter 3: Heat, Work and Energy

2. Definitions Force Work: motion against an opposing force dw = - f dxExamples: spring, gravity Conservative Force: absence of friction Energy: capacity to do work Kinetic En: by virtue of motion; K = ½ mv 2 Potential En: by virtue of position; V Total (Internal) Energy: E = K + V

3. Law of Conservation of Energy (First Law) The internal energy of an isolated system is constant; is an invariant of motion. ΔE = 0 = q + w = heat plus work In an isolated system, no energy or matter is exchanged with the surroundings. Other conserved properties are mass and momentum’ they cannot be created or destroyed but can flow.

4. Heat Interesting historical theories about heat. Heat, q, can flow, is not conserved, is related to the temperature change of matter.

5. Kinetic Theory of Gases Matter = particles (atoms, molecules) that move through space. Heat is the exchange of energy due to motions and collisions of particles. Collisions are assumed to be elastic (limit of ideal case) During collisions, energy and momentum are exchanged. As a result, a piston may move (work is done) or heat can be transferred to the surroundings. In either case, q decreases.

6. KTG (2) Electromagnetic radiation can influence the motions of molecules (radiant heat) Mechanical model on a microscopic scale Explains many macroscopic observations: IGL, P, diffusion rates, η, κ,, velocity of sound in a gas… In 3 dimensions, = 3/2 kT = ½ m 2

7. KTG + QM = Improved Model QM  energy levels are quantized; the population or occupancy number, N i, of each level depends on T and the set of ε i. The internal total energy is U = Σ N i ε i

8. Heat Flows to Maximize W Ex 3.3 and Fig 3.7 conclude that W increases with U. Ex 3.4 and Fig 3.9 explains that heat flow maximizes W. (And the flow continues until the two temps are identical.) Ex 3.5 shows that max W is not associated with equal final energies.

9. Second Law of Thermodynamics Systems tend toward their states of maximum multiplicity. The entropy of the universe is increasing. Carnot Cycle: no perpetual motion machines; you cannot convert all heat to work because there is always residual heat loss.