Bubbles In a Pot of Boiling Water Contain

TP Bubbles in a pot of boiling water contain … 1. 2. 3. 4. 5. 6. Only O2 𝑔 and N2 𝑔 Only H2O 𝑔 Only air H2O 𝑔 and air All of the above equally None of the above • Vapor pressure: Liquid-vapor equilibrium • Vapor pressure and boiling point • Phase diagrams Next lecture: Complete phase diagrams; Ch11: Solutions: Vapor pressure lowering, 𝑃 𝑥 𝑃° ; Boiling point elevation, 𝑇 𝑇° 𝐾 𝑚 ; Freezing point depression, 𝑇° 𝑇 𝐾 𝑚 ; Osmotic pressure, Π 𝑅𝑇𝑀 ; 1 1 2 TP Bubbles in a pot of boiling water contain … Liquid-vapor equilibrium 1. 2. 3. 4. 5. 6. 6 6 Only O2 𝑔 and N2 𝑔 Only H2O 𝑔 Only air H2O 𝑔 and air All of the above equally None of the above 7 7 1 Equilibrium vapor pressure Equilibrium vapor pressure Sketch what is going on at the surface at this point. Sketch what is going on at the surface now. 8 8 9 9 Equilibrium vapor pressure Equilibrium vapor pressure Sketch how pressure must change with temperature. Vapor pressure must rise with temperature. 10 10 11 11 2 Equilibrium vapor pressure Evaporation Vapor pressure rises with temperature. Vapor pressure must rise with temperature. Why is this so? 12 12 13 13 Evaporation Evaporation Vapor pressure rises with temperature. 𝑇 𝑇 60.0℃, 𝑃 78.3℃, 𝑃 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℃? 351 Torr 𝑇 760 Torr 14 14 60.0℃, 𝑃 351 Torr, 𝑅 0.0820575 15 15 3 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 351 Torr, 𝑅 0.0820575 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 351 Torr 17 17 18 18 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 𝑛 351 Torr, 𝑅 0.0820575 846 Torr, calculated from ideal gas law 𝑃 351 Torr 19 19 60.0℃, 𝑃 𝑛 0.0163 mol, calculated from molar mass 𝑃 351 Torr 0.00675 mol, calculated from ideal gas law, using 𝑃 𝑇 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 20 20 4 Evaporation Vapor pressure and boiling point 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℃? Boiling means “bubbles”. 𝑇 60.0℃, 𝑃 𝑛 0.0163 mol, calculated from molar mass 𝑃 351 Torr, 𝑅 846 Torr, calculated from ideal gas law Bubbles form only if they are able to hold back the liquid walls. 𝑃 0.00675 mol, calculated from ideal gas law, using 𝑃 𝑛 𝑛 0.0163 mol 0.00675 mol This means bubbles only exist if the vapor pressure is the same as the pressure acting on the liquid surface. 351 Torr 𝑛 𝑛 Bubbles are pure vapor of the liquid. 0.0820575 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. 21 21 22 22 TP The order of normal boiling points lowest to highest is … Vapor pressure and boiling point Substance 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? 1. 2. 3. 4. 5. 23 23 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 Normal 1 atm boiling point/℃ 100 diethyl ether acetone ethanol ethanol acetone diethyl ether acetone diethyl ether ethanol ethanol diethyl ether acetone something else 24 24 5 Vapor pressure and boiling point Relative normal boiling point, Tb The normal boiling point is the temperature at which bubbles form at 1 atm. 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? 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 What do you predict for relative vapor pressures of these substances at 200°C? 25 25 26 26 TP The substance with the lowest vapor pressure substances at 200°C is … 1. 2. 3. 4. Phase diagrams CH4 NH3 HCl N2 Lines of 𝑃 versus 𝑇 at which different phases are present at the same time. That is, values of 𝑃 and 𝑇 at which different phases are in equilibrium. 28 27 27 28 6 Phase diagrams What about the intersection marked “A” 29 29 30 30 Triple point Supercritical fluid Liquid tert-butyl alcohol, C CH3 3OH, can boil and freeze at the same time... Supercritical transition of liquid Cl2 … 31 31 32 32 7