1. Lecture 1: Energy Reading: Zumdahl 9.1 Outline –Energy: Kinetic and Potential –System vs. Surroundings –Heat, Work, and Energy

2. Energy: Kinetic vs. Potential Potential Energy (PE) –Energy due to position or composition. –Equals (mgh) in example. Kinetic Energy (KE) –Energy due to motion. –Equals mv 2 /2 in example.

3. Energy = KE + PE Energy is the sum of kinetic energy and potential energy. Energy is readily interconverted between these two forms. If the system of interest is isolated (no exchange with surroundings), then total energy is constant.

4. Example: Mass on a Spring Initial PE = 1/2 kx 2 At x = 0: –PE = 0 –KE = 1/2mv 2 =1/2kx 2 Units of Energy Joule = kg.m 2 /s 2 Example: –Init. PE = 10 J –M = 10 kg –Vmax = [2(PE)/M] 1/2 = 1.4m/s 0

5. First Law of Thermodynamics First Law: Energy of the Universe is Constant E = q + w (remember this) q = heat. Transferred between two bodies of differing temperature. Note: q ≠ Temp! w = work. Force acting over a distance (F x d)

6. Applying the First Law Need to differentiate between the system and surroundings. System: That part of the universe you are interested in (i.e., you define it). Surroundings: The rest of the universe.

7. Conservation of Energy Total energy is conserved. Energy gained by the system must be lost by the surroundings. Energy exchange can be in the form of q, w, or both.

8. Heat Exchange: Exothermic Exothermic Reaction. Chemical process in which system evolves resulting in heat transfer to the surroundings. q < 0 (heat is lost)

9. Another Example of Exothermic

10. Heat Exchange: Endothermic Endothermic Reaction: Chemical process in which system evolves resulting in heat transfer to the system. q > 0 (heat is gained)

11. Another Example of Endothermic

12. Energy and Sign Convention If system loses energy: E final < E initial E final -E initial =  E < 0. If system gains energy: E final > E initial E final -E initial =  E > 0.

13. Heat and Work Sign Convention If system gives heat q < 0 (q is negative) If system gets heat q > 0 (q is positive) If system does work w < 0 (w is negative) If work done on system w > 0 (w is positive)

14. Example: Piston Figure 9.4, expansion against a constant external pressure No heat exchange: q = 0 System does work: w < 0 (adiabatic)

15. Example (cont.) How much work does the system do? P ext = force/area |w| = force x distance = P ext x A x  h = P ext  V w = - P ext  V (note sign)

16. Example 9.1 A balloon is inflated from 4 x 10 6 l to 4.5 x 10 6 l by the addition of 1.3 x 10 8 J of heat. If the balloon expands against an external pressure of 1 atm, what is  E for this process? Ans: First, define the system: the balloon.

17. Example 9.1 (cont.)  E = q + w = (1.3 x 10 8 J) + (-P  V) = (1.3 x 10 8 J) + (-1 atm (V final  V init )) = (1.3 x 10 8 J) + (-0.5 x 10 6 l.atm) Conversion: 101.3 J per l.atm (-0.5 x 10 6 l.atm) x (101.3 J/l.atm) = -5.1 x 10 7 J

18. Example 9.1 (cont.)  E = (1.3 x 10 8 J) + (-5.1 x 10 7 J) = 8 x 10 7 J (Ans.) In English: the system gained more energy through heat than it lost doing work. Therefore, the overall energy of the system has increased.

19. Constant Volume Processes  For a constant volume process, the change in internal energy of the system is equal to the heat transferred. What if the volume of the system is held constant?  E = q + w = q V 0 “constant V”