University:
Boston University
Course:
CAS CH 102 | General Chemistry 2
Academic year:

2021
Views:

98

Pages:

5
Author:

Houston Watkins

TP The order of normal boiling points is … Substance 20% 20% 20% 20% 20% 1. 2. 3. 4. 5. Vapor pressure at 25 ˚C, kPa Acetone, CH3C O CH3 30.8 Diethyl ether, CH3CH2 2O 71.7 Ethanol, CH3CH2OH 7.87 Water, H2O 3.17 Normal 1 atm boiling point ˚C For today … • Vapor pressure and boiling 100 diethyl ether acetone ethanol ethanol acetone diethyl ether acetone diethyl ether ethanol ethanol diethyl ether acetone something else Equilibrium vapor pressure Boiling means “bubbles” Bubbles are pure vapor of the liquid 1 Pa force/area 1 kg m/s2 / m2 1 kg m 1 bar 100 kPa exactly 1 atm 101.325 kPa exactly 1 s 2 1 Equilibrium vapor pressure Equilibrium vapor pressure Low temperature ⟶ Few particles in vapor ⟶ Low equilibrium vapor pressure Equilibrium vapor pressure Higher temperature ⟶ More particles in vapor ⟶ Higher equilibrium vapor pressure Equilibrium vapor pressure Normal boiling temperature ⟶ Maximum particles in vapor ⟶ 1 atm equilibrium vapor pressure 2 Vapor pressure and boiling point Vapor pressure and boiling The normal boiling point is the temperature at which bubbles form at 1 atm. Vapor pressure rises with temperature. Can we make bubbles and so “boil” at a lower temperature? Let’s see … Vapor pressure and boiling Vapor pressure and boiling Bubbles appear when vapor pressure Bubbles appear when vapor pressure applied pressure “Normal” boiling point is when vapor pressure is exactly 1 atm 101.325 kPa applied pressure A vacuum pump allows boiling at lower temperature. 3 Vapor pressure and boiling Bubbles appear when vapor pressure Vapor pressure and boiling point applied pressure The normal boiling point is the temperature at which bubbles form at 1 atm. What do you predict for relative boiling points of these substances? A pressure cooker delays boiling to higher temperature. Vapor pressure at 25 ˚C, kPa Substance TP The order of normal boiling points is … Substance 20% 20% 20% 20% 20% 1. 2. 3. 4. 5. Vapor pressure at 25 ˚C, kPa Acetone, CH3C O CH3 30.8 Diethyl ether, CH3CH2 2O 71.7 Ethanol, CH3CH2OH 7.87 Water, H2O 3.17 diethyl ether acetone ethanol ethanol acetone diethyl ether acetone diethyl ether ethanol ethanol diethyl ether acetone something else Acetone, CH3C O CH3 30.8 Diethyl ether, CH3CH2 2O 71.7 Ethanol, CH3CH2OH 7.87 Water, H2O 3.17 Normal 1 atm boiling point ˚C 100 Vapor pressure and boiling point Normal 1 atm boiling point ˚C The normal boiling point is the temperature at which bubbles form at 1 atm. What do you predict for relative boiling points of these substances? 100 Substance Vapor pressure at 25 ˚C, kPa Acetone, CH3C O CH3 3: 30.8 Normal 1 atm boiling point ˚C 3: 56 Diethyl ether, CH3CH2 2O 4: 71.7 4: 35 Ethanol, CH3CH2OH 2: 7.87 2: 78 Water, H2O 1: 3.17 1. 100 4 Relative normal boiling point, Tb The normal boiling point is the temperature at which bubbles form at 1 atm. Quiz The substance with the lowest vapor pressure substances at 200 °C is … 25% 25% 25% 25% 1. 2. 3. 4. CH4 NH3 HCl N2 What do you predict for relative vapor pressures of these substances at 200 °C? 5