Lecture 11/1/98, Chapter 6, Section 3-4

Announcements

Changes of State

1. Heat of fusion (333 J gm^-1)
2. Heat of vaporization 2260 J gm^-1)
3. 10 gram of water from 200 K to 400 K
   1. C_ice = 2.1 J gm^-1 K^-1
   2. [delta]H_fusion = 333 J gm^-1
   3. C_water = 4.2 J gm^-1 K^-1
   4. [delta]H_vap = 2260 J gm^-1
   5. C_steam = 2.0 J gm^-1 K^-1

      State	Start Temp	Final Temp	Energy
      Ice	200 K	273.15 K	1536 J
      Melt	273.15	273.15	3330 J
      Liquid	273.15	373.15	4200 J
      Boil	373.15	373.15	22600 J
      Steam	373.15	400	537 J
      TOTAL			32203 J

Introduction to Enthalpy

1. q = heat (Thermal Energy)
2. w = work (P*V, change in volume, N=kg m sec^-2, Pa=kg m^-1 sec^-2)
3. [delta] E = q + w (Energy is heat plus work)
4. IF volume is constant, no work, [delta] E = q
5. IF pressure is constant, [delta] H = q_p

Concept of Change, Altitude Analogy

1. Arbitrary Reference Point (sea level)
2. Sign is significant
3. Independent of Path
4. Introduce Energy Level Diagram

Calculation of [delta] H_rxn

1. Misc terms
   1. [delta] H Change in Enthalpy
   2. [delta] H° Change in Enthalpy at standard state
   3. [delta] H_f° Enthalpy of Formation at standard state
   4. Standard State 25C (298K) and 1 bar
2. [delta] H_rxn = H_final - H_initial
3. Energy Diagram
4. State Properties
   1. quantities
   2. pressure
   3. temperature
   4. volume
   5. physical state (ie: solid or liquid)
5. Hess's Law (sum of steps).
   1. Use energy level diagram C (s) + 2 H₂ -> CH₄

      Reaction	[delta] Hrxn (kJ)
      C (s) + O2 (g) -> CO2 (g)	-373.51
      H2 (g) + 1/2O2 (g) -> H2O (l)	-285.83
      CH4 (g) + 2 O2 (g) -> CO2 (g) + 2 H2O (l)	-890.37

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