Chemistry Lecture Notes

Chemistry Lecture Notes - Chemistry Lecture Notes 1...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Chemistry Lecture Notes January 15, 2008 1. Equilibria- Balance between stability of lower enthalpy (heat energy) and higher entropy (disorder). 2. Physical Equilibria- Phase Transitions ( no “chemistry”), state with the lowest free energy is the most stable, therefore at high temperature the state with the highest delta S (disorder) will be the most stable. Gibbs Free Energy Equation 3. Different liquids have different vapor pressures. 4. Dynamic equilibrium is established once rate of evaporation equals the rate of condensation. 5. When comparing different liquids what matters is the free energy of the vapor compared to the liquid. 6. For almost all substances the difference in delta S ENTROPY between the vapor and the liquid is the same! Delta S = 85 J K per mol Therefore the diversity in liquid properties is dominated by the delta H, ENTHALPY of vaporization. 7. Molecules with higher enthalpy of vaporization are molecules with OH groups that have higher molecular weights. 8. The stronger the intermolecular forces the lower the vapor pressure. 9. Intermolecular forces lead to the enthalpy difference between the liquid and the vapor. The larger the IMF, the higher delta H vaporization, enthalpy. The larger the delta H vaporization the smaller the vapor pressure. The smaller the vapor pressure the higher the boiling point. 10. Vapor Pressure does not depend on the volume! If you try to change the pressure by changing the volume, you just change the condensation Vs evaporation until it goes to
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
11. Temperature is the only thing that affects vapor pressure! As temperature goes up V.P. goes up incredibly fast. Boiling point (in an open container in a room) is the temperature at which the V.P. is equal to 1 atm. More standard definition boiling point is where vapor pressure equals atmospheric pressure. Experiment 2 nd day- He boiled water by placing it in a vacuum, he didn’t need heat at all, with no atmosphere the water was able to boil. 12. The Clausseus-Clapeyron Equation relates the vapor pressure at two temperatures to the enthalpy of vaporization. January 17, 2008 1. Reminder: Boiling Point is when the vapor pressure is higher than the total pressure. 2. Shaving cream experiment- higher pressure inside air pockets no pressure outside shaving cream expands. The Claussius-Clapeyron Equation ln (P2/P1) = -delta H vaporization/R times (1/T2 – 1/T1) It relates the vapor pressure at temperature T1 to the vapor pressure P2 at temp. T2. PROBLEM: What is the boiling point of water? Given the vapor pressure of water at 25%C is 24 Torr and delta H vaporization = 40.8 kJ/mol. WORK: P= 1 atm which is 760 Torr At what T2 is P2 = 760 Torr? 3. Phase transitions happen at a specific pressure.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 06/09/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.

Page1 / 9

Chemistry Lecture Notes - Chemistry Lecture Notes 1...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online