Complete IMFs Determine Relative Boiling Points

Why is HCl < HBr < HI? • Complete: IMFs determine relative boiling points • Practice: Boiling points and enthalpy of vaporization • Vapor pressure: Liquid-vapor equilibrium • Vapor pressure and boiling point TP The correct order of polarity of HBr, HCl and HI is least to most … 1. 2. 3. 4. 5. 6. HBr HCl HBr HI HCl HBr HCl HI HI HCl HI HBr HI HCl HI HBr HBr HCl TP The correct order of boiling point of HBr, HCl and HI is lowest to highest … 1. 2. 3. 4. 5. 6. HBr HCl HBr HI HCl HBr HCl HI HI HCl HI HBr HI HCl HI HBr HBr HCl 1 Permanent dipoles Induced dipoles Sketch a second molecule arranged so that it … attracts maximally repels maximally Why is HCl < HBr < HI? Sketch the induced dipole in each case: neither attracts nor repels Why is NH3 > PH3 < AsH3 < SbH3? 2 Why is OH2 > FH > NH3? TP Identify the compound with the smallest energy of vaporization kJ/mol . 1. 2. 3. 4. water ethanol dimethyl ether hexane Why is FH > NH3? TP The correct order of boiling point of CH3OH, CH4, and S C O lowest to highest is … 1. 2. 3. 4. 5. CH3OH CH4 S C O S C O CH4 CH3OH CH4 S C O CH3OH CH4 CH3OH S C O some other order 3 TP The correct order of boiling point of CH3Br, CH2Br2, CH3Cl, and CH2Cl2 lowest to highest is … 1. 2. 3. 4. 5. 6. CH2Br2 CH2Cl2 CH3Br CH2Cl2 CH2Br2 CH3Cl CH3Cl CH3Br CH2Cl2 CH3Br CH3Cl CH2Br2 CH3Cl CH3Br CH2Br2 some other order CH3Cl CH3Br CH2Br2 CH2Cl2 CH2Cl2 TP Bubbles in a pot of boiling water contain … 1. 2. 3. 4. 5. 6. Liquid-vapor equilibrium Equilibrium vapor pressure Only O2 𝑔 and N2 𝑔 Only H2O 𝑔 Only air H2O 𝑔 and air All of the above equally None of the above Sketch what is going on at the surface at this point. 4 Equilibrium vapor pressure Equilibrium vapor pressure Sketch what is going on at the surface now. Sketch how pressure must change with temperature. Equilibrium vapor pressure Equilibrium vapor pressure Vapor pressure must rise with temperature. Vapor pressure must rise with temperature. Why is this so? 5 Evaporation Evaporation Vapor pressure rises with temperature. Vapor pressure rises with temperature. 𝑇 𝑇 60.0℃, 𝑃 78.3℃, 𝑃 351 Torr 760 Torr Evaporation Evaporation A 0.750-gram sample of ethanol CH CH OH is placed in a sealed 400-mL container. Is there any liquid present when the temperature is held at 60℃? A 0.750-gram sample of ethanol CH CH OH is placed in a sealed 400-mL container. Is there any liquid present when the temperature is held at 60℃? 𝑇 60.0℃, 𝑃 𝑛 ?, calculate from molar mass 𝑃 351 Torr, 𝑅 0.0820575 ?, calculate from ideal gas law, 𝑃𝑉 60.0℃, 𝑃 𝑛 0.0163 mol, calculated from molar mass 351 Torr, 𝑅 0.0820575 𝑛𝑅𝑇 𝑛 ?, calculate from ideal gas law, using actual pressure, 𝑃 𝑛 𝑛 𝑛 𝑇 ? 32 6 Evaporation Evaporation A 0.750-gram sample of ethanol CH CH OH is placed in a sealed 400-mL container. Is there any liquid present when the temperature is held at 60℃? A 0.750-gram sample of ethanol CH CH OH is placed in a sealed 400-mL container. Is there any liquid present when the temperature is held at 60℃? 𝑇 60.0℃, 𝑃 𝑛 0.0163 mol, calculated from molar mass 𝑃 846 Torr, calculate from ideal gas law 351 Torr, 𝑅 0.0820575 𝑃 𝑇 60.0℃, 𝑃 𝑛 0.0163 mol, calculated from molar mass 𝑃 351 Torr 𝑛 351 Torr, 𝑅 0.0820575 846 Torr, calculated from ideal gas law 𝑃 351 Torr 0.00675 mol, calculated from ideal gas law, using 𝑃 351 Torr Evaporation Evaporation A 0.750-gram sample of ethanol CH CH OH is placed in a sealed 400-mL container. Is there any liquid present when the temperature is held at 60℃? A 0.750-gram sample of ethanol CH CH OH is placed in a sealed 400-mL container. Is there any liquid present when the temperature is held at 60℃? 𝑇 60.0℃, 𝑃 𝑛 0.0163 mol, calculated from molar mass 𝑃 351 Torr, 𝑅 0.0820575 846 Torr, calculated from ideal gas law 𝑃 0.00675 mol, calculated from ideal gas law, using 𝑃 𝑛 𝑛 𝑛 0.0163 mol 0.00675 mol 0.0096 mol 60.0℃, 𝑃 𝑛 0.0163 mol, calculated from molar mass 𝑃 351 Torr 𝑛 𝑇 351 Torr 351 Torr, 𝑅 0.0820575 846 Torr, calculated from ideal gas law 𝑃 351 Torr 𝑛 0.00675 mol, calculated from ideal gas law, using 𝑃 𝑛 𝑛 𝑛 0.0163 mol 0.00675 mol 351 Torr 0.0096 mol Note, we have ignored the slight increase in vapor volume because of the decrease in liquid volume due to evaporation. 7 Vapor pressure and boiling point Vapor pressure and boiling point Boiling means “bubbles”. The normal boiling point is the temperature at which bubbles form at 1 atm. Bubbles are pure vapor of the liquid. What do you predict for relative boiling points of these substances? Bubbles form only if they are able to hold back the liquid walls. This means bubbles only exist if the vapor pressure is the same as the pressure acting on the liquid surface. TP The order of normal boiling points lowest to highest is … 1. 2. 3. 4. 5. Substance Vapor pressure at 25℃, 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 Normal 1 atm boiling point/℃ Vapor pressure and boiling point 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℃, kPa Normal 1 atm boiling point/℃ Acetone, CH3C O CH3 3: 30.8 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 8 Relative normal boiling point, Tb The normal boiling point is the temperature at which bubbles form at 1 atm. TP The substance with the lowest vapor pressure substances at 200°C is … 1. 2. 3. 4. CH4 NH3 HCl N2 What do you predict for relative vapor pressures of these substances at 200°C? 9