CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 1 IN OUR PREVIOUS UH LECTURE WE WERE LOOKING AT THE BONDING FORCES BETWEEN

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1 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 1 CHM 105/106 Program 38: Unit 4 Lecture 9 IN OUR PREVIOUS UH LECTURE WE WERE LOOKING AT THE BONDING FORCES BETWEEN MOLECULES IN LIQUIDS CALLED THE INTERMOLECULAR FORCES BECAUSE IN LIQUIDS THINGS ARE EXISTING AS MOLECULES. WE TALKED ABOUT THE THREE MAJOR CATEGORIES: HYDROGEN BONDING, WHICH OF COURSE IS RATHER SELECTIVE BECAUSE IT INVOLVES ONLY UH COMPOUNDS THAT HAVE HYDROGEN WHICH IS ATTACHED TO OXYGEN NITROGEN OR FLUORINE. WE HAVE DIPOLE-DIPOLE FORCES WHICH EXIST IN MOLECULES THAT ARE PERMANENTLY POLAR, AND THEN WE HAVE LONDON OR DISPERSION FORCES WHICH EXIST IN ALL TYPES OF MATTER IN OTHER WORDS IN ALL TYPES OF MOLECULAR LIQUIDS. ONE OF THE PHYSICAL PROPERTIES ASSOCIATED WITH LIQUIDS IS WHAT WE CALL THEIR VAPOR PRESSURE AND VAPOR PRESSURE IS ONE OF THE PROPERTIES WHICH IS DEPENDENT UPON THEN THESE INTERMOLECULAR FORCES. WE TALKED JUST A LITTLE BIT ABOUT HOW VAPOR PRESSURE ARISES YESTERDAY AS WE TOOK A LOOK AT THIS DRAWING AND WE INDICATED THAT IF WE STARTED OUT WITH A CONTAINER AND PLACED SOME LIQUID IN IT AS WE SEE IN THE FIRST DRAWING HERE WE WOULD NOTICE THAT WE HAD ZERO AS FAR AS THE PRESSURE GAUGE. HOWEVER, AFTER SOME TIME WE WOULD NOTE THAT A PRESSURE DOES EXIST, MEANING THAT SOME OF THE MOLECULES HAVE ESCAPED FROM THE LIQUID AND ARE IN THE GASEOUS PHASE IN ORDER TO EXERT PRESSURE IN THE CONTAINER. THE PROCESS OF THE MOLECULES ESCAPING FROM THE LIQUID INTO THE GASEOUS PHASE IS REFERRED TO AS EVAPORATION. BUT THERE IS ALSO A REVERSE PROCESS THAT CAN OCCUR., AFTER WE HAVE SOME MOLECULES IN THE GASEOUS PHASE SOME OF THEM MIGHT STRIKE THE LIQUID SURFACE AND RE-STICK, GO BACK INTO THE LIQUID STATE AND WE REFER TO THAT PROCESS AS CONDENSATION. WE SAID THAT AFTER SOME TIME THE PRESSURE GAUGE WILL REMAIN A CONSTANT, MEANING THEN THAT THE RATE OF EVAPORATION HAS BECOME EQUAL TO THE RATE OF CONDENSATION. IN OTHER WORDS, THE KINETIC MOTION OF THE MOLECULES IS STILL CONTINUING ON, BUT AT A RATE THEN IN SUCH THAT THE RATE AT WHICH MOLECULES LEAVE THE LIQUID NOW BECOMES EQUAL TO THE RATE AT WHICH THEY RETURN. AND WHEN WE REACH THAT PARTICULAR

2 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 2 CONDITION WE REFER TO THAT AS THE VAPOR EQUILIBRIUM VAPOR PRESSURE OF THE LIQUID. NOW THE EQUILIBRIUM, OF COURSE THAT MEANS BECAUSE WE HAVE TWO OPPOSITE PROCESSES GOING ON IN EQUAL MAGNITUDE VAPOR PRESSURE IS THE PRESSURE EXERTED BY THE GASEOUS MOLECULES THE EQUILIBRIUM VAPOR PRESSURE OF A LIQUID IS TEMPERATURE DEPENDENT AND SO IN OTHER WORDS IT S NOT THE SAME AT ALL TEMPERATURES. SO IF WE LOOK AT AGAIN THE EFFECT OF TEMPERATURE ON VAPOR PRESSURE FOR A PARTICULAR SUBSTANCE WE FIND THAT AS TEMPERATURE INCREASES VAPOR PRESSURE LIKEWISE INCREASES. WHAT THIS GRAPH IS POINTING OUT THAT IN FACT THE CHANGE IN VAPOR PRESSURE IS NOT A LINEAR. SO WE LL PUT AN X THROUGH THAT. IT S NOT A LINEAR RELATIONSHIP IT S AN EXPONENTIAL RELATIONSHIP. SO AS TEMPERATURE GOES UP IT STARTS OUT CHANGING VERY SLOWLY BUT THEN THE VAPOR PRESSURE BEGINS TO RISE VERY RAPIDLY AND WE CAN FURTHER STATE THAT VAPOR PRESSURE OF A LIQUID IS DIRECTLY PROPORTIONAL TO TEMPERATURE. SO IN OTHER WORDS THERE IS A DIRECT RELATIONSHIP BETWEEN THE TWO, AND OF COURSE THE VAPOR PRESSURE THEN HOW EASILY MOLECULES CAN ESCAPE FROM THE LIQUID GOES BACK TO THE THESE INTERMOLECULAR FORCES: HYDROGEN BONDING, DIPOLE- DIPOLE AND LONDON DISPERSION FORCES. NOW ONE OTHER THING THAT WE CAN SAY, WELL LET ME COME BACK TO THAT IN JUST A SECOND. LET S TAKE A LOOK AT FOUR REPRESENTATIVE COMPOUNDS HERE AND LOOK AT THEIR VAPOR PRESSURE. THIS WOULD BE THE VAPOR PRESSURE AT A PARTICULAR TEMPERATURE AND I BELIEVE THE TEMPERATURE HERE IS I RECALL 20 CELSIUS DEGREES. NOTICE THAT THIS IS THE MOLAR MASS. IF WE WERE TO LOOK AT WATER WHICH HAS VERY LITTLE MASS TO THE MOLECULES. ONE WOULD PREDICT OR OR AT LEAST SUSPECT THAT WATER MOLECULES COULD ESCAPE VERY EASILY AND IF THAT WERE TRUE THEN WATER SHOULD HAVE A VERY HIGH VAPOR PRESSURE, BUT NOTICE THAT EVEN THOUGH IT IS THE LIGHTEST MOLECULE IT HAS THE LOWEST VAPOR PRESSURE OF THE FOUR LIQUIDS GIVEN. NOW THE REASON FOR THAT IS THAT WHEN WE LOOK AT WATER REMEMBER WE SAID THAT WATER HAS HYDROGEN BONDING SO IF WE TALK ABOUT WATER WE HAVE HYDROGEN BONDING POSSIBLE AND OF COURSE IT IS A POLAR MOLECULE SO IT ALSO HAS DIPOLE-DIPOLE INTERACTION AND EVERYTHING HAS LONDON FORCES. SO THE BONDING

3 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 3 FORCES IN WATER MOLECULES IS VERY HIGH, VERY STRONG INTERMOLECULAR FORCE, THEREFORE WATER MOLECULES CANNOT ESCAPE VERY EASILY. OKAY, SO WE HAVE A VERY LOW VAPOR PRESSURE FOR WATER AS COMPARED TO ITS MASS. NOW WE WOULD SUSPECT THAT THE HEAVIEST MOLECULE CARBON TETRACHLORIDE WOULD BE THE HARDEST FOR MOLECULES TO ESCAPE, BECAUSE THEY RE BIGGER. THEY RE HEAVIER, MORE MASS-MASS, MATTER-MATTER ATTRACTION. BUT AGAIN WE SEE THAT S NOT THE CASE. IT S NOT THE HIGHEST, I MEAN IT S NOT THE LOWEST VAPOR PRESSURE. WATER IS LOWER, EVEN METHANOL WHICH IS ABOUT 5 TIMES SMALLER IN MASS HAS A VAPOR PRESSURE ABOUT THE SAME. WELL IF WE LOOKED AT CARBON TETRACHLORIDE, WHAT WE FOUND WHEN WE LOOKED AT IT AS FAR AS GEOMETRY ET CETERA IS A TETRAHEDRAL MOLECULE. IT S NON-POLAR, SO IT DOESN T HAVE ANY DIPOLE-DIPOLE FORCES. T OBVIOUSLY CAN T HAVE ANY HYDROGEN BONDING BECAUSE THERE S NO HYDROGEN IN IT AND SO THE ONLY FORCE THAT EXISTS IN THE CARBON TETRACHLORIDE THEN ARE THE LONDON FORCES AND THAT S THE REASON THAT EVEN THOUGH IT HAS A VERY HIGH MASS IT HAS A RELATIVELY HIGH VAPOR PRESSURE. IT S STILL PRETTY EASY FOR CARBON TETRACHLORIDE MOLECULES TO ESCAPE. OKAY, ALSO CARBON TETRACHLORIDE IS RATHER COMPACT, AND COMPACT MOLECULES HAVE LOWER DISPERSION FORCES THAN SPREAD-OUT TYPE OF MOLECULES. NOTICE THE PENTANE HERE, EVEN THOUGH IT S ONLY HALF AS HEAVY IT HAS A MUCH HIGHER VAPOR PRESSURE. AGAIN NO HYDROGEN BONDING INVOLVED IN IT ET CETERA. SO WE SEE THAT TO KNOW OR PREDICT SOMETHING ABOUT VAPOR PRESSURE OF A SUBSTANCE WE NEED TO KNOW SOME THING ABOUT THE INTERMOLECULAR FORCES, AND THAT S WHERE IT COMES IN AND LOOKING AT THE GEOMETRY LOOKING AT HYDROGEN BONDING, LOOKING AT POLARITY ALL COMES INTO PREDICTING WHAT TYPE OF VAPOR PRESSURE ONE WOULD HAVE. ALRIGHT, NOW IF WE GO BACK TO OUR VAPOR PRESSURE CHART FOR JUST A SECOND, WE HAD HERE, AND LET S SUPPOSE THAT THIS POINT RIGHT HERE REPRESENTED 760 TORR. THIS TEMPERATURE THEN IF WE GO OVER HERE, THIS TEMPERATURE DOWN HERE CORRESPONDING TO THAT IS REFERRED TO AS THE NORMAL BOILING POINT. NOW, WHAT DO WE MEAN FIRST OF ALL BY BOILING? WHAT IS BOILING? BOILING IS THE RAPID EVOLUTION IF THE VAPOR OF GASEOUS STATE FROM A LIQUID. THAT S

4 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 4 WHAT BOILING IS. WHEN WE SEE WATER BOIL IT S THE RAPID EVOLUTION, THE BUBBLES ARE FULL OF GASEOUS WATER MOLECULES. THAT S WHAT THE BUBBLES ARE THAT WE SEE RISING. SO THE RAPID EVOLUTION OF THE GASEOUS PHASE FROM THE LIQUID IS REFERRED TO AS BOILING. NORMAL BOILING IS, OR NORMAL BOILING POINT, IS THE TEMPERATURE AT WHICH A LIQUID BOILS WHEN ITS EQUILIBRIUM VAPOR PRESSURE EQUALS ONE ATMOSPHERE OR 760 TORR. BUT A MATERIAL WILL BOIL, A LIQUID CAN BOIL AT NEARLY TEMPERATURE BECAUSE BOILING IS DEPENDENT UPON THE APPLIED PRESSURE. ANY TIME, ANY TIME THAT THE EQUILIBRIUM VAPOR PRESSURE, AND WE LL JUST CALL IT VAPOR PRESSURE, ANY TIME THE VAPOR PRESSURE IS EQUAL TO THE APPLIED PRESSURE BOILING OCCURS. SO THEREFORE IF WE LOWER THE APPLIED PRESSURE, NOTICE IF I WERE TO COME DOWN THIS GRAPH AND LET S SAY IF I WERE TO APPLY A PRESSURE DOWN HERE NOW ABOUT A FIFTH OF WHAT WE HAD SO WE LL SAY 150 TORR, IF I APPLY A PRESSURE OF 150 TORR TO THIS LIQUID IT S GOING TO BOIL WAY DOWN HERE. THAT WOULD BE ITS BOILING POINT AT THE PRESSURE THAT WE ARE APPLYING. SO BOILING, WHEN WE TALK ABOUT BOILING, BOILING IS A PHENOMENON RELATED TO THE APPLIED PRESSURE. IF WE WANT TO FORCE SOMETHING TO BOIL AT A HIGHER TEMPERATURE THAN NORMAL, THAN ITS NORMAL BOILING POINT, WE CAN INCREASE THE APPLIED PRESSURE. HAS ANYONE HERE EVER COOKED USING A PRESSURE COOKER OR PRESSURE COOKER PAN? NO ONE HAS? ALRIGHT, WELL WE CAN USE A PRESSURE COOKER TO DO EXACTLY THAT, TO APPLY A GREATER PRESSURE, A PRESSURE GREATER THAN 760 TORR SO THAT WE CAN ACTUALLY FORCE THE WATER TO BECOME WARMER THAN 100 CELSIUS DEGREES BEFORE IT BOILS. IF WE CAN DO THAT, IF WE CAN GET THE WATER TO 120 DEGREES BEFORE IT BEGINS BOILING OBVIOUSLY THEN WE CAN COOK FOOD QUICKER AND THIS IS THE PURPOSE THEN IN USING A PRESSURE COOKER. AS A MATTER OF FACT, IF YOU LIVED AT A HIGHER ELEVATION, IF YOU WERE TO TRY TO COOK SOMETHING LET S SAY ON PIKE S PEAK YOU WENT CAMPING, YOU WENT HIKING AND YOU STAYED OUT ON PIKE S PEAK AND YOU WANTED TO COOK SOMETHING AND YOU REMEMBERED THAT WELL TO COOK A POTATO IT SHOULD TAKE ABOUT 45 MINUTES IN BOILING WATER AND SO YOU PUT UP YOUR FIRE, YOUR CAMP FIRE AND YOU PUT THE PAN ON FULL OF WATER, THROW THE POTATOES IN AND BOIL IT LIKE MAD AND

5 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 5 POUR THE WATER OFF AND CUT THE POTATO. IN 45 MINUTES IT S JUST AS SOLID AS CAN BE. IT S HOT, IT D PROBABLY BE ABOUT 95 CELSIUS DEGREES, BUT IT S NOT COOKED BECAUSE THE CONVERSION OF THE STARCH IN THE POTATO REQUIRES A TEMPERATURE OF ABOUT 98 CELSIUS DEGREES. WATER BOILS AT ABOUT 95 OR 94 DEGREES ON TOP OF PIKES PEAK. YOU CAN T CONVERT THE STARCH, YOU DON T HAVE A TEMPERATURE NECESSARY TO CARRY OUT THE CHEMICAL CHANGE, AND YOUR FOOD WOULD BASICALLY BE HOT BUT STILL RAW. IF YOU WERE GOING TO DO A BOILED EGG AND YOU THREW EGGS IN AND COOKED IT FOR FIVE MINUTE AND YOU BROKE THEM OPEN YOU WOULD HAVE NOTHING BUT A HOT UNCOOKED EGG, RAW EGG, BECAUSE THE WHITE PART OF THE EGG TAKES A TEMPERATURE AGAIN VERY NEAR 98 CELSIUS DEGREES TO UNDERGO THE CHEMICAL CHANGE THAT GIVES US THE COOKED APPEARANCE TO AN EGG. SO PEOPLE LIVING AT HIGHER ELEVATION OFTEN HAVE TO USE A PRESSURE COOKER IN ORDER TO CARRY OUT THE COOKING PROCESS. TO GET THE WATER UP TO AT LEAST 100 DEGREES SO THAT THE COOKING CAN OCCUR. AGAIN, BOILING IS GOING TO OCCUR ANY TIME THAT WE REACH THAT SET OF CONDITIONS FOR THE VAPOR PRESSURE AND THE APPLIED PRESSURE HAVE BECOME EQUAL BOILING IS GOING TO OCCUR. AS A MATTER OF FACT, WE CAN BY REDUCING THE PRESSURE, W E CAN ACTUALLY GET WATER SOLUTIONS TO BOIL AT VERY LOW TEMPERATURES. IF YOU TALK ABOUT INSTANT COFFEE, IT S OFTEN CALLED FREEZE-DRIED. FREEZE DRIED INSTANT COFFEE. WHEN INSTANT COFFEE WAS FIRST PRODUCED THE WAY THEY WOULD MAKE IT WAS MAKE IT WAS BASICALLY BREW UP A POT OF COFFEE, POUR IT INTO A PAN, SET IT ON A STOVE OR SOMETHING HOT AND EVAPORATE THE WATER OFF. WELL WHAT THAT LET YOU THEN WAS COFFEE, SOLID COFFEE PARTICLES, THE DISSOLVED MATERIALS THAT WERE IN THERE AND YOU GRIND IT UP AND PUT IT BACK INTO HOT WATER AND HAVE A CUP OF COFFEE. BUT THE COFFEE THAT YOU GOT FROM THE FIRST INSTANT COFFEES TASTED ABOUT LIKE THE COFFEE DOES AFTER IT HAS BEEN IN A POT ALL DAY LONG AND PLUGGED IN NICE AND HOT. ANYONE THAT IS A COFFEE DRINKER KNOWS WHAT I M TALKING ABOUT. THE COFFEE AFTER 12 HOURS IS SITTING IN A COFFEE POT IS NOT THE SAME FLAVOR AS THE COFFEE THAT WAS BREWED INITIALLY BECAUSE THE TEMPERATURE CAUSES MANY OF THE FLAVORING CHEMICALS TO UNDERGO A CHANGE WHICH GIVES IT A TOTALLY

6 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 6 DIFFERENT FLAVOR, AND THE EARLY INSTANT COFFEES DID NOT TASTE LIKE FRESH BREWED COFFEE. FREEZE DRIED COFFEE NOW, WHAT THEY DO NOW IS THEY MAKE A POT OF COFFEE UP, QUICKLY BEGIN COOLING IT AND THEN AS THEY COOL IT THEY ALSO REDUCE THE APPLIED PRESSURE, AND AS THEY REDUCE THE APPLIED PRESSURE THE COFFEE CONTINUES TO BOIL MEANING THAT THE LIQUID WATER IS ESCAPING RAPIDLY UNTIL FINALLY WE GET IT TO THE POINT THAT WATER IS ACTUALLY ESCAPING AS IT FREEZES, AND AS IT FREEZES IT STILL LOSES THE WATER BECAUSE WE HAVE VERY LITTLE PRESSURE ABOVE IT BUT WE END UP WITH NOW ARE CRYSTALS WHICH HAVEN T UNDERGONE THIS CONSTANT HEATING PROCESS, AND THEREFORE WHEN WE RECONSTITUTE IT BY ADDING HOT WATER WE DO GET A CUP OF COFFEE THAT TASTES CLOSER TO FRESH BREWED COFFEE. THERE S STILL SOME CHANGE HAS OCCURRED. SO WE CAN USE THIS PRINCIPLE HERE THEN BY CHANGING THE APPLIED PRESSURE WE CAN CHANGE WHAT TEMPERATURE A MATERIAL BOILS AT. OKAY, NOW IF WE WERE TO LOOK AT WHAT HAPPENS AS WE HEAT, OKAY ONCE AGAIN BOILING, WHEN VAPOR PRESSURE EQUALS APPLIED PRESSURE. IF WE WERE TO LOOK AT WHAT HAPPENS TO TEMPERATURE AS WE BEGIN HEATING A LIQUID WE WOULD SEE SOMETHING THAT LOOKS LIKE THIS. WE WOULD SEE THAT AS WE BEGAN TO HEAT THE LIQUID THE TEMPERATURE WOULD RISE. FOR INSTANCE, IF WE PUT A GLASS OF WATER OR CUP OF WATER INTO A PAN AND MEASURED ITS INITIAL TEMPERATURE. ITS INITIAL TEMPERATURE MIGHT BE ABOUT 20 CELSIUS DEGREES ROOM TEMPERATURE. THEN WE TURN ON THE STOVE, WE TURN ON THE FLAME AND WHAT HAPPENS IS THE WATER TEMPERATURE BEGINS TO RISE. BUT THEN FINALLY WE REACH THE POINT THAT IT BEGINS TO BOIL, THE PHASE CHANGE, AS IT GOES FROM A LIQUID TO A GAS EVAPORATION. AND ONCE WE REACH THE BOILING POINT ALL OF THE ENERGY THAT GOES IN FROM HERE ON OUT GOES IN TO THE PHASE CHANGE. NOTICE THERE S NO LONGER A TEMPERATURE CHANGE AS WE REACH THE PHASE CHANGE. ALL OF THE ENERGY GOING I IS NOW BEING USED TO CONVERT LIQUID TO GAS AND THE TEMPERATURE WOULD REMAIN A CONSTANT UNTIL WE FINALLY HAD CONVERTED ALL OF THE LIQUID TO GAS, THEN WE COULD ACTUALLY BEGIN HEATING THE GAS ITSELF. NOW THIS JUST POINTS OUT ONE THING. IF I M COOKING THEN, THE MOST EFFICIENT ENERGY WISE FOR COOKING WOULD BE TO GET THE WATER JUST TO ITS

7 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 7 BOILING POINT AND JUST BARELY MAINTAIN M INIMUM BOILING, BECAUSE CRANKING UP THE HEAT ISN T GOING TO DO ANYT HING TO RAISE THE TEMPERATURE. WE RE AT THE HIGHEST TEMPERATURE WE CAN GET. ALL WE RE GOING TO DO IS BOIL THE WATER OFF FASTER, DRY THE PAN OUT AND BURN THE FOOD IN THE PAN WHILE WE RE NOT PAYING ATTENTION. ALRIGHT, SO ONCE YOU GET IT BOILING YOU MIGHT AS WELL CONSERVE ON ENERGY. CUT IT DOWN AS LOW AS YOU CAN TO JUST MAINTAIN THE BOILING BECAUSE THE TEMPERATURE S GOING TO MAINTAIN A CONSTANT UNTIL ALL OF THE LIQUID HAS EVAPORATED. ALRIGHT, NOW THE AMOUNT OF ENERGY NEEDED TO CHANGE THEN ONE MOLE OF SUBSTANCE FROM ITS LIQUID TO GASEOUS STATE AT ITS BOILING POINT IS REFERRED TO AS THE MOLAR HEAT OF VAPORIZATION. THE MOLAR HEAT OF VAPORIZATION IS THE ENERGY NEEDED TO CHANGE ONE MOLE OF LIQUID TO GA S AT ITS BOILING POINT. IN OTHER WORDS THIS DOESN T INVOLVE ANY HEATING, JUST MERELY THE PHASE CHANGE PA RT. THE REVERSE PROCESS IS MOLAR HEAT AT CONDENSATION, HOWEVER WE USUALLY USE ONLY ONE TABLE. WE CALL IT THE SAME THING REGARDLESS OF WHICH DIRECTION WE RE GOING. HOWEVER, ONE WAY ENERGY IS BEING PUT IN, SO WHEN WE RE VA PORIZING SOMETHING W E RE PUTTING ENERGY IN, THAT S ENDOTHERMIC. WE TALKED ABOUT THAT BEFORE. AND IF IT S CONDENSING ENERGY MUST BE GIVEN OFF, AND THAT S AN EXOTHERMIC PROCESS. BUT THE MAGNITUDE, THE AMOUNT OF ENERGY, IS THE SAME WHETHER WE RE EVAPORATING OR CONDENSING WE RE GOING TO HAVE THE SAME AMOUNT OF ENERGY CHANGE PER ONE MOLE OF SUBSTANCE. NOW, THE MOLAR HEAT OF VAPORIZATION SORT OF CORRESPONDS AGAIN TO THESE INTERMOLECULAR FORCES. THE STRONGER THE FORCES THE MORE DIFFICULT IT IS TO TEAR IT APART INTO THE GAS AND THEREFORE THE HIGHER THE ENERGY REQUIREM ENT. AGAIN IF WE TA KE A LOOK AT SOME TABULAR VALUES HERE WE HAVE SOME MOLAR HEATED VAPORIZATION FOR THREE LIQUIDS HERE ETHANOL OR ETHYL ALCOHOL, AMMONIA, AND WATER. AND NOTICE THAT EVEN THOUGH WATER IS THE UH, ONE OF THE SMALLEST MASS-WISE OF THE MOLECULES HERE IT HAS THE HIGHEST, IT HAS THE HIGHEST MOLAR HEATED VAPORIZATION. TO CHANGE 18 GRAMS OF WATER, THAT S ABOUT 18 MILLILITERS, TO CONVERT 18 MILLILITERS OF WATER FROM A LIQUID TO A GAS AT 100 CELSIUS DEGREES. WE VE ALREADY HEATED IT THERE. IT WILL REQUIRE 40.7

8 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 8 KILOJOULES OF ENERGY. 18 GRAMS OF WATER WOULD REQUIRE 40.7 KILOJOULES OF ENERGY TO CHANGE IT FROM LIQUID TO GAS. OKAY, AND KILO OF COURSE M EANS A THOUSAND SO THAT S 40.7 THOUSAND JOULES OF ENERGY IN THE PROCESS. ALRIGHT, MOLAR HEAT OF VAPORIZATION, AND BY THE REVERSE PROCESS, WHEN A MOLE OF WATER, 18 GRAMS OF WATER, GOES FROM STEAM FROM GASEOUS WATER BACK TO LIQUID IT RELEASES 40.7 KILOJOULES OF ENERGY. THIS IS WHY WATER IS USED AS A HEAT TRANSFER SYSTEM. IT S VERY EFFECTIVE. IT CARRIES A LOT OF HEAT. FOR INSTANCE, THIS BUILDING, IN THE COLD TIME OF THE YEAR IS HEATED BY TRANSPORTING GASEOUS WATER, WHICH WE CALL STEAM, FROM A POWER PLANT THAT IS PRODUCING IT. WE HAVE BOILERS THAT ARE CONVERTING THE WATER TO STEAM, THE STEAM COMES THROUGH A SET OF PIPES TO THE BUILDING IT THEN GOES THROUGH COILS WHERE IT CONDENSES BACK TO LIQUID WATER AND EVERY 18 GRAMS OF STEAM THAT COMES OVER TO THE BUILDING IS GOING TO GIVE OFF 40.7 JOULES KILOJOULES OF ENERGY AS IT GOES BACK TO THE LIQUID. WE TAKE THE HOT WATER, RUN IT BACK THROUGH THE PIPE TO THE BOILER AND REHEA T IT, CONVERT IT TO STEAM, RUN THE STEAM, AND WE CAN DO THIS FOR AN INFINITE LENGTH OF TIME. ALSO, THIS IS WHY A STEAM BURN IS SO SEVERE IN CONTRAST TO JUST A HOT WATER BURN. FOR INSTANCE, THE AMOUNT OF ENERGY TO CHANGE ONE GRAM OF WATER ONE CELSIUS DEGREE IS UH, JOULES, OKAY. THAT S THE AMOUNT OF, THAT S JOULES, NOT KILOJOULES, SO FOR 18 GRAMS OF WATER TO CHANGE ONE DEGREE, IN OTHER WORDS IF I PUT SOME HOT WATER ON MY SKIN AND IT CHANGED FROM 100 TO 99 THEN I WOULD HAVE 18 TIMES THIS OR WE LL JUST CALL IT ABOUT 90 JOULES OF ENERGY. BUT IF I HAVE 18 GRAMS OF STEAM THAT HITS MY SKIN AND CONDENSES, EVEN WITHOUT CHANGING TEMPERATURE I AM GOING TO RELEASE 40,700 JOULES OF ENERGY. THAT S A LOT OF HEAT ENERGY. THAT S WHY STEAM IS SO SEVER IN TERMS OF A BURN, TREMENDOUS AMOUNT OF HEAT OF CONDENSATION OR HEAT OF VAPORIZATION. ALRIGHT, WELL WE CAN USE THESE OF COURSE TO DO SOME QUANTITATIVE CALCULATIONS, AND LET S JUST DO ONE HERE QUICKLY. LET S CALCULA TE THE NUMBER OF KILOJOULES OF ENERGY THAT WOULD BE NEEDED TO VAPORIZE 100 GRAMS OF AMMONIA AT ITS NORMAL BOILING POINT. IN OTHER WORDS IT S ALREADY AT THE BOILING POINT, NOW WE RE GOING TO DO THE

9 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 9 PHASE CHANGE PART. AND IN ORDER TO CALCULATE IT THE TERM THAT WE OFTEN USE ARE THE LETTERS Q. Q STANDS FOR HEAT ENERGY AND SO OFTEN WE LL SEE IT JUST WRITTEN AS Q. Q WILL BE EQUAL TO 100 GRAMS OF AMMONIA MULTIPLIED BYT HEN THE AMOUNT OF ENERGY, THE MOLAR HEAT OF VA PORIZATION, FOR AMMONIA WHICH WAS 23.5 KILOJOULES PER MOLE. BUT WE CAN SEE THAT MY UNITS DON T WORK OUT RIGHT THERE BECAUSE OBVIOUSLY GRAMS CANNOT CANCEL MOLES SO WE NEED TO BRING IN ONE OTHER FACTOR. THAT IS, WE HAVE TO CONVERT THIS FROM GRAMS TO MOLES. SO WE CAN MULTIPLY BY ONE MOLE AF AMMONIA OVER ITS MASS WHICH WOULD BE 14 PLUS THREE SO THAT WOULD BE GRAMS, AND SO NOW THE GRAMS OF AMMONIA CANCEL, THE MOLES OF AMMONIA CANCEL AND WE RE LEFT WITH UNITS OF KILOJOULES. WELL LET S SEE WE WOULD HAVE 100 DIVIDED BY AND MULTIPLIED BY WE WOULD HAVE KILOJOULES OF ENERGY TO CONVERT 100 GRAMS TO ITS VAPOR OR VICE VERSA. IF 100 GRAMS OF AMMONIA CONDENSED WE WOULD GET THAT AMOUNT OF ENERGY RELEASED. AMMONIA IS USED AS A REFRIGERANT. WE TALKED A LITTLE BIT ABOUT THIS WHEN WE TALKED ABOUT THE HALOGENATED HYDROCARBONS, THE FREONS. THE FREONS WHICH REPLACED AMMONIA AS REF RIGERANTS, BUT BOTH ARE GOOD REFRIGERANTS BECAUSE THEY RE RELATIVELY EASILY LIQUEFIED AND VAPORIZED AND BOTH OF THEM HAVE FAIRLY HIGH MOLAR HEATS OF VAPORIZATION. FOR INSTANCE IF I DO HAVE AMMONIA AS MY REFRIGERANT THEN AS IT MOVES THROUGH THE REFRIGERATOR FIRST OF ALL IT GOES INTO A COMPRESSOR AND IN THE COM PRESSOR WE LIQUEFY IT AND FOR EVERY HUNDRED GRAMS OF AMMONIA THAT WE LIQUEFIED WE D GIVE OFF KILOJOULES OF ENERGY. IF WE VE EVER FELT ON THE BACKSIDE OF THE REFRIGERATOR OR FREEZER OR AN AIR CONDITIONER IT S VERY WARM. THE REA SON IT S WARM IS WE RE SQUEEZING THAT HEAT OUT OF THE REFRIGERANT. AS WE RE-LIQUEFY IT THAT ENERGY, THAT ENERGY, THAT MOLAR EAT OF VAPORIZATION HAS TO BE RELEASED. NOW, NOW WE HAVE THE AMMONIA AS A LIQUID. WHAT DO WE DO? WE LET THE LIQUID AMMONIA NOW WHICH IS UNDER A PRESSURE UP THROUGH SOME COILS IN THE REFRIGERATOR, AND AS IT MOVES INTO THE COILS WHERE THE PRESSURE IS LESS IT DOES WHAT? GOES FORM A LIQUID BACK TO A GAS. NOW IN ORDER TO GO FROM A LIQUID TO A GAS WHAT DOES IT HAVE TO DO? IT HAS TO GAIN KILOJOULES OF

10 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 10 ENERGY FOR EVERY 100 GRAMS OF AMMONIA THAT GOES BACK TO THE GAS. WHERE S IT GONNA GET THAT HEAT? FROM THE FOOD THAT I PUT IN THE REFRIGERATOR. WHEN IT GETS BACK IT CIRCULATES BACK, IT S NOW A GAS. IT GOES BACK TO THE COMPRESSOR. WE JUST SQUEEZE IT AGAIN, AND WHEN WE SQUEEZE IT AND PUT IT BACK TO A LIQUID IT GIVES THE ENERGY OFF, AND THIS GOES THROUGH AND THROUGH AND THROUGH. A HEAT PUMP DOES THE REVERSE PROCESS. WE DO THE SQUEEZING SO THAT THE HEAT ENERGY IS RELEASED INSIDE AND WE TAKE THE ENERGY, IN OTHER WORDS THE COIL NOW IS OUTSIDE AND WE EXTRACT HEAT FROM EI THER WATER FROM THE GROUND OR THE AIR. AND WE THEN HAVE THE GAS OR THE AMMONIA BEING CONVERTED TO A GAS OUTSIDE AND WE RE COMPRESSING IT AND RELEASING THE HEAT TO THE INSIDE. SO ACTUALLY A HEAT PUMP IS ACTUALLY MORE THAN A REFRIGERATOR BEING HOOKED UP IN REVERSE ORDER. SO INSTEAD OF THE HEAT BEING THE WASTE MATERIAL IT S NOW THE POSITIVE PART. ALRIGHT, OKAY. WELL ANOTHER PROPERT Y OF LIQUIDS IS A PROPERTY THAT WE CALL VISCOSITY. VISCOSITY IS THE RESISTANCE TO FLOW. SO IF SOMETHING IS VISCOUS, IF IT S HIGHLY VISCOUS IT MEANS THAT IT HAS A HIGH RESISTANCE TO FLOW. WE SAY SOMETHING ABOUT BEING SLOWER THA N MOLASSES IN JANUARY. ALRIGHT, W ELL MOLASSES ITSELF IS VERY VISCOUS. IF YOU TRY TO POUR MOLASSES OUT OF A BOTTLE EVEN AT ROOM TEMPERATURE IT S PRETTY SLOW. OKAY, IT DOESN T FLOW VERY READILY IT HAS A RESISTANCE TO FLOW, AND IF WE COOL IT DOWN THAT RESISTANCE TO FLOW BECOMES EVEN GREATER. TYPICALLY, THIS IS EXACTLY WHAT WE FIND FOR ALL THINGS, THAT VISCOSITY INCREASES AS TEMPERATURE DECREASES SO THAT IT FLOWS WITH LESS ABILITY AT A LOWER TEMPERATURE. THAT S WHY WE RE SAYING SLOWER THAN MOLASSES IN JANUARY BECAUSE IF YOU WENT OUT ON A COLD JANUARY MORNING AND TRIED TO POUR MOLASSES OUT OF A JAR IT JUST DOESN T FLOW. ALRIGHT, NOW THAT S A PROBLEM WHEN WE TALK ABOUT LUBRICATING IN AUTOMOBILE ENGINES. BECAUSE WHAT WE WOULD LIKE IS WE WOULD LIKE TO HAVE A LUBRICANT THAT WAS RATHER VISCOUS WHEN THE ENGINE WAS HOT TO PREVENT WEAR, BUT YET VISCOSITY OF THINGS DECREA SES AS THINGS GET HOT. SO WHEN WE PUT OIL IN AN AUTOMOBILE FOR INSTANCE FIRST OF ALL IF THE ENGINE IS COLD THE OIL IS FAIRLY VISCOUS, IT S FAIRLY THICK. AND AS THE ENGINE WARMS UP THE

11 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 11 OIL BECOMES LESS VISCOUS, IT BECOMES MORE RUNNY AND IT DOESN T LUBRICATE AS WELL AND SO THAT S A PROBLEM. WELL IN THE EA RLY DAYS OF OIL WE WOULD HAVE THINGS LIKE THIS. WE WOULD HAVE AN OIL, WE SOMETIMES CALL IT A WEIGHT, IT S ALSO REFERRED TO AS AN SAE NUMBER. THAT S THE SOCIETY OF AUTOMOTIVE ENGINEERS ARE THE ONES THAT HAVE CALIBRATED THESE SAE. UH, IF YOU HAD AN OIL THAT SAID HD 30. TAT MEANS THAT IT HAS A CERTAIN VISCOSITY AT ROOM TEMPERATURE, AT NORMAL TEMPERATURE, ALRIGHT, BUT THAT VISCOSITY CHANGES AS THE ENERGY, OR THE TEMPERATURE IN THE ENGINE CHANGES. NOW, IF YOU LIVED I NA VERY COLD COUNTRY THIS BECOMES A PROBLEM. IF I USE 30 WEIGHT THAT MEANS IT S A LITTLE VISCOUS. THAT MEANS IT LUBRICATES THE ENGINE WELL, BUT ON A VERY COLD MORNING THAT OIL IS GOING TO BE SO VISCOUS IT S GOING TO BE VERY DIFFICULT TO TURN THE CAR ENGINE OVER. WE VE GOT A LOT OF DRAG NOW AND IT S DIFFICULT TO GET THE CAR ENGINE TO EVEN TURN OVER. SO PEOPLE THAT LIVED IN NORTHERN CLIMATES EARLY IN THE AUTOMOBILE HISTORY WOULD USE THEN SOMETHING LIKE A OIL OF 30 OR 40 IN THE SUMMER WHEN IT WAS HOT, AND THEN COMES WINTER THEY WOULD DRAIN IT ALL OUT AND PUT IN AN OIL THAT WAS LIKE WHAT WE CALL A FIVE OR A TEN. NOW A FIVE OR A TEN MEANS THAT AT COLD TEMPERATURES IT S STILL FAIRLY RUNNY. AT HIGH TEMPERATURES IT BECOMES VERY RUNNY. BUT IF YOU W ERE IN A COLD CLIMATE YOU PROBABLY DIDN T WORRY AS MUCH ABOUT THE CA R LUBRICATION ON THE WARM END AS YOU DID BEING ABLE TO START IT ON A MORNING WHEN IT WAS 40 BELOW ZERO. AND SO YOU WOULD USE AN OIL THAT WAS LIKE A TEN OR A FIVE WEIGHT OIL. SO YOU CHANGED TWICE A YEAR. CHANGED GOING INTO WINTER, CHANGED GOING INTO SUMMER. SUMMER TO GIVE YOU BETTER LUBRICANT, LUBRICANT TO GIVE YOU EASIER STARTING, LESS DRAG ON THE ENGINE. WELL, WE CAN SEE HERE THREE OILS THAT SHOW VARIABLE NUMBER. THE FIRST ONE THERE SAYS 10 DASH 30. GUESS I CAN T GET THAT REAL CLEAR. NEXT ONE 10 DASH 40, AND ANOTHER ONE OVER HERE 20 DASH 50. NOW, WE TALKED ABOUT POLYMERS, POLYMERIZATION IN CHAPTER SEVEN. CHEMISTS HAVE FIGURED OUT WAYS THAT WE CAN ADD CERTAIN CHEMICAL ADDITIVES THAT BEING TO POLYMERIZE AS TEMPERATURE GOES UP. NOW THAT MEANS THAT WE TAKE SMALL MOLECULES SITTING IN THE OIL AND WHEN IT S COLD THERE IS INDIVIDUAL MOLECULES. AS IT

12 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 12 GETS WARM THESE INDIVIDUAL UNSATURATED M OLECULES BEGIN TO POLYMERIZE THEY BEGIN TO HOOK TOGETHER, AND WHEN THEY HOOK TOGETHER THEY MAKE BIGGER MOLECULES THE VISCOSITY INCREASES. AND SO WHAT THIS NUMBER IMPLIES HERE IS THAT WHEN THIS OIL IS COLD IT WILL HAVE A VISCOSITY OF ABOUT TEN. MEANING THE ENGINE HAS AN EASY START BECAUSE THE OIL IS NOT VERY VISCOUS. AS THE ENGINE TEMPERATURE INCREASES THE OIL VISCOSITY ACTUALLY INCREASES TO 30, WHEN NORMALLY THE OIL VISCOSITY WOULD DECREASE, THE OIL VISCOSITY NOW IS INCREASING, AND SO NOW AT HIGH TEMPERATURES WE GET THE SAME LUBRICATING THAT WE WOULD WITH A 30 WEIGHT OIL, BUT WHEN IT S COLD WE HA VE THE LESS VISCOUS EASY STARTING PROPERTY OF THE OIL AT A TEN WEIGHT OIL. SO INSTEAD OF NEEDING TO CHANGE YOUR OIL TWICE A YEAR AND PUTTING IN A TEN IN THE WINTER AND A FORTY IN THE SUMMER WE CAN USE A MIXED OIL, A VARIABLE WEIGHT OIL TO HANDLE THE ENTIRE YEAR AROUND. SO VISCOSITY IS RESISTANCE TO FLOW AND IN THE CASE OF THE OILS OF COURSE IT CAN BE ADJUSTED BY ADDING PARTICULAR CHEMICALS AND MOST OF THE OILS WE SEE TODAY ON THE MARKET ARE ACTUALLY A VARIABLE WEIGHT. OCCASIONALLY YOU STILL WOULD WANT TO USE, IF YOU WERE USING SA Y A A LAWN MOWER. YOU NORMALLY AREN T GOING TO MOW IN THE WINTER TIME, AND SO YOU DON T WORRY TOO MUCH ABOUT THE STARTING PART BECAUSE YOU RE GOING TO BASICALLY DO IT IN WARM WEATHER ANYWAY AND IF THAT S THE CASE THEN YOU WOULD USE AN OIL THAT GIVES YOU MORE OF A CONSTANT LUBRICATION WHICH WOULD BE SOMETHING LIKE A 30 OR A 40 WEIGHT OIL. SO THERE ARE STILL TIMES WHEN WE WANT TO USE JUST SINGLE TYPE OF VISCOSITY OILS, BUT FOR AUTOMOBILES TODAY MOST OF IT IS IN FORM OF THE VARIABLE. NOW ONE OTHER PROPERTY OF LIQUIDS IS OCCURS AT THE TOP OF THE LIQUID. LET ME JUST SAY THIS HERE, I LL SAY VISCOSITY IS WHAT WE CALL A BULK PROPERTY. BY THAT WE M EAN THAT THE VISCOSITY IS THE SAME THROUGH THE ENTIRE THING. THE OTHER PHENOMENON WE RE GOING TO TALK ABOUT IS CALLED SURFACE TENSION. AND SURFACE TENSION IS THEN A SPECIAL PROPERTY OF LIQUIDS THAT OCCURS ONLY NEAR THE SURFACE OF THE LIQUID. IF WE WERE TO LOOK AT A LA YER OF LIQUID THE MOLECULES SITTING UP HERE FOR INSTANCE DO NOT HAVE ANYTHING TO ATTRACT THEM UPWARD. IF WE TOOK A MOLECULE HERE IT S

13 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 13 ATTRACTED TO MOLECULES IN ALL DIRECTIONS. MOLECULES UP HERE CANNOT BE ATTRACTED TO ANYTHING ABOVE, A ND SO BASICALLY THEIR ONLY ATTRACTION ARE FOR THINGS DOWN THIS DIRECTION. NOW WHAT THAT DOES THEN IS IT COMPRESSES THIS TOP LAYER. SO THIS TOP LAYER THEN BECOMES M ORE DENSE THAN THE BULK OF THE LIQUID. SO THERE S A COMPRESSION FACTOR IN THE TOP LAYERS, TOP ROWS OF THE LIQUID. A S A MATTER OF FACT, THIS, THIS COMPRESSED LAYER, THIS MORE DENSE LAYER CAN ACTUA LLY BECOME QUITE DENSE. IN THE CASE OF WATER WHICH HAS HYDROGEN BONDING, POLAR-POLAR BONDS, ET CETERA, VERY STRONG INTERMOLECULAR FORCES, THE SURFACE TENSION ON WATER IS QUITE STRONG. IT S THE SURFACE TENSION OF WATER FOR INSTANCE THAT ACCOUNTS FOR WATER BEADING UP WHEN WE PUT IT ONTO A WAXED SURFACE. THE WATER MOLECULES LIKE THEMSELVES SO WELL THAT ON THE SURFACE THEY BEGIN ATTRACTING INWARD AND THEY JUST PULL INTO A DROP SHAPE, SO THEY BEAD UP. ALRIGHT, THE STRENGTH OF THIS, AS I SAID, CAN BE RELATIVELY GREAT. IF WE LOOK AT INSECTS, AQUATIC TYPE INSECTS LIKE MOSQUITOES FOR INSTA NCE, AND WE NOTICE THEY CAN STAND ON WATER. NOTICE HERE IF YOU CAN SEE THIS HOW (NOT AUDIBLE) THE LEGS ARE. LET ME SLIDE THIS OVER A LITTLE BIT. SEE WHERE THE LEGS ARE HERE, SETTING ON THE WATER HOW IT IS ACTUALLY CAVED IN SOMEWHAT. IT S JUST LIKE TAKING A PIECE OF PAPER, THIS FILM, ON TOP OF THE WATER IS SITTING THERE AND WHERE THE LEG IS IS COMPRESSING IT A LITTLE BIT BUT IT S NOT BREAKING THROUGH. THE DENSITY OF THAT TOP LAYER OF WATER IS DENSE ENOUGH TO SUPPORT THE MASS OF THE INSECT ON TOP OF IT. NOW IF YOU WERE TO TAKE THAT MOSQUITO AND PUT IT DOWN IN THE WATER IT WOULD SINK BECAUSE ITS DENSITY IS GREATER, BUT ITS DENSITY IS NOT GREATER THAN THE DENSITY OF THE SURFACE TENSION ITSELF. THAT SURFACE TENSION MAY BE SEVERAL HUNDRED TIMES GREATER THAN THE BULK DENSITY OF THE SOLUTION. IT S ACTUALLY, ONE IS ACT UALLY ABLE TO SUPPORT A PIECE OF IRON. IRON HAS A DENSITY OF FOUR OR FIVE GRAMS PER CUBIC CENTIMETER. WATER IS ONE, SO IT S FIVE TIMES MORE DENSE THA N WATER, AND YOU CAN ACTUALLY PUT A PIECE OF STEEL ON TOP OF A PIECE OF WATER AND IT WON T SINK. IF YOU RE CAREFUL NOT TO BREAK THE SURFACE TENSION. NOW WE CAN BREAK THE SURFACE TENSION. WE CAN DESTROY THAT INTERACTION

14 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 14 OF THE WATER MOLECULES IF WE PUT IN ANOTHER TYPE OF MOLECULE THAT WILL INTERFERE WITH WATER ATTRACTING WATER. THESE ARE REFERRED TO AS SURFA CTANTS, OR WE CALL THEM SOAPS. THE REASON WE USE A SOAP PARTLY IS TO BREA K DOWN THIS BEADING EFFECT. IF YOU EVER, IF YOU EVER PUT WATER ON A SOAPY SURFACE IT SPREADS OUT INSTEAD OF BEADS UP. THE REASON IT SPREADS OUT IS BECAUSE THE SOAP, THE SOAP MOLECULES INTERFERE WITH THE WATER-WATER MOLECULE INTERACTION AND WEAKEN THE SURFACE TENSION SO THAT IT TENDS TO JUST SPREAD OUT INSTEAD OF BEAD UP. IF WE WERE TO PUT SOME SOAP IN WATER THE INSECT WOULD SINK BECAUSE WE VE DESTROYED THE SURFACE TENSION LAYER. AS A MATTER OF FACT, THAT S ONE OF THE WAYS THAT INSECTS, ESPECIALLY MOSQUITOES, ARE CONTROLLED IN AREAS WHERE WE DON T WANT TO USE PESTICIDES BUT WE DON T WANT THEM TO BE ABLE TO HATCH AND WE STILL HAVE SMALL PONDS OF WATER OR WHATEVER. WE CAN ADD A SURFACTANT. WHEN MOSQUITOES, AS LARVA THEY RE IN THE WATER AND THEY UNDERGO THEIR CHANGE THEY LITERALLY CRAWL OUT ON TOP OF THE SURFACE TENSION AND DRY OFF, AND A MOSQUITO HAS TO DRY OFF SO THAT IT, FINALLY IT S WINGS WILL BE ABLE TO WORK AND IT CAN FLY OFF SOMEPLACE AND LOOK FOR ME FOR A MEAL. AND IF WE DISRUPT THIS SURFACE TENSION LAYER IT CAN T GET ON THE SURFACE AND IT WILL DROWN. IT WILL UNDERGO ITS CHANGE BUT IT WOULD NEVER BE ABLE TO ESCAPE THE WATER AND IT WOULD DIE OF STARVATION OR NOT BEING ABLE TO GET AIR EITHER WAY, AND SO WE CAN KILL OR CONTROL THE INSECT. SO USING SOAP OR SURFACTANT MATERIALS IS ONE OF THE WAYS THAT WE CAN HELP CONTROL THE MOSQUITO POPULA TION, AND I SHOULD SAY IN AREAS THAT WE DON T WANT TO USE PESTICIDES OR WE MIGHT HAVE SMALL PONDS OF STANDING WATER THAT INSECT HATCHING COULD OCCUR, THIS IS ONE WAY TO CONTROL IT. ALRIGHT, WELL JUST A BOUT OUT OF TIME HERE BUT LETS GO AHEAD AND MENTION JUST QUICKLY HERE IN OUR NEXT LECTURE WE RE GOING TO SPEND ADDITIONAL TIME LOOKING AT SOLIDS AND SOME OF THE INTERMOLECULAR FORCES THERE AND WE RE GOING TO LOOK AT FOUR DIFFERENT TYPES OF SOLIDS. WE RE GOING TO LOOK AT MOLECULAR SOLIDS, IONIC SOLIDS, METALLIC SOLIDS, AND COVALENT SOLIDS. AND WE LOOKED AT SOME OF THE PROPERTY DIFFERENCES, WHAT ACCOUNTS FOR THE PROPERTY DIFFERENCES OF THESE FOUR

15 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 15 TYPES THEN OF SOLIDS. WELL WE CAN GO ON HERE QUICKLY BECAUSE THIS RELATES AO CLOSELY TO WHAT WE TALKED ABOUT IN LIQUIDS AND THAT IS THE MOLECULAR SOLIDS. THE MOLECULAR SOLIDS, BECAUSE AGAIN WE RE TA LKING ABOUT MOLECULES AS UNITS HERE, BEHAVE JUST LIKE LIQUIDS. SO ANY OF THE FORCES THAT WE TALKED ABOUT IN LIQUIDS ARE ALSO THE FORCES THAT WE TALKED ABOUT IN THE SOLIDS. IN OTHER WORDS, IF WE TALK ABOUT WATER IN THE SOLID STATE WE RE GOING TO HAVE THE SAME FORCES INVOLVED THAT WE HAVE IN WATER IN A LIQUID STATE. WE RE GOING TO HAVE HYDROGEN BONDING. WE RE GOING TO HAVE DIPOLE-DIPOLE, WE RE GOING TO HAVE LONDON FORCES. IF WE TALKED ABOUT SOLID CARBON TETRACHLORIDE. WE RE GOING TO TALK ABOUT A NON-POLAR MOLECULE, NO HYDROGEN BONDING. THE ONLY FORCES WOULD BE THE LONDON FORCES. OKAY, SO MOLECULAR SOLIDS HAVE THE SAME INTERPARTICLE FORCES AS LIQUIDS, SAME TYPE OF FORCES, AND HERE WE SEE THEN FOUR DIFFERENT SOLIDS HERE. CAN T SEEM TO FIND A AVERAGE FOCUS HERE, BUT WE HAVE IODINE, CARBON DIOXIDE, WATER AND SUCROSE. THIS IS SUGAR MOLECULE DOWN HERE, TABLE SUGA R. THE NUMBER ON THE LEFT-HAND SIDE REPRESENTS THE MOLAR MASS. AGAIN WE HAVE WATER 18, CARBON DIOXIDE 44, SUGAR 342, AND THE IODINE MOLECULE254. BUT THIS ONE, IODINE, STRICTLY NON-POLAR, NO HYDROGENS, SO THE ONLY THING IT CAN HAVE IS LONDON FORCES. CARBON DIOXIDE AS A SOLID. CARBON DIOXIDE AS A SOLID OF COURSE IS WHAT WE CALL DRY ICE. AGAIN IT S A NON-POLAR MOLECULE. THIS IS PART OF THE PURPOSE OF DRAWING LEWIS STRUCTURES AND GEOMETRIC SHAPES. IT S A NON-POLAR MOLECULE. WATER, POLAR MOLECULE HYDROGEN BONDING AND OF COURSE THIS ONE HAS HYDROGENS ATTACHED TO OXYGENS. IF WE DREW OUT, DIDN T TRY TO DRAW OUT THE STRUCTURE FOR THIS BUT IF WE DID WE D HAVE A LOT OF HYDROGEN BONDS AND SO WE D HAVE AGAIN STRONG FORCES THERE. NOW THESE TWO PARTICULAR MATERIALS, AND ESPECIALLY THIS ONE UNDERGO A PROCESS WHICH IS CALLED SUBLIMATION. SUBLIMATION IS THE DIRECT PHASE CHANGE FROM SOLID TO A GAS WITH NO LIQUID STATE. NOW MOST THINGS GO FROM SOLID, IF WE HEAT THEM UP THEY GO TO A LIQUID IF WE HEAT THEM UP THEY FINALLY GO TO A GAS. BUT THERE ARE SOME MATERIALS THAT HAVE THE ABILITY TO GO DIRECTLY FROM THE SOLID STATE TO THE GASEOUS STATE AND THIS IS CALLED

16 CHM 105 & 106 MO1 UNIT FOUR, LECTURE NINE 16 SUBLIMATION. CARBON DIOXIDE GOES DIRECTLY FROM A SOLID TO A GAS, THAT S WHY IT S CALLED DRY ICE. SOLID CARBON DIOXIDE LOOKS A LOT LIKE ICE, LOOKS LIKE A CLOUDY LOOKING ICE, ICE IN TERMS OF BEING FROZEN WATER. BUT IN THE CASE OF WATER IF WE RE GOING TO USE IT AS A REFRIGERANT IT S GOING TO GO FROM SOLID STATE, IT WOULD MELT AND THEN IT WOULD BE A LIQUID AND OF COURSE OBVIOUSLY IF YOU RE GOING TO TRY AND PACK THINGS WITH THIS YOU VE GOT WATER A GAINST CARDBOARD OR PAPER AND IT S SOGGY AND THE BOXES FALL APART NOT GOOD. BUT IF W E USE DRY ICE AS THE CARBON DIOXIDE ABSORBS HEAT FROM THE FOOD, KEEPING IT FROZEN, IT GOES DIRECTLY TO A GAS WITH NO LIQUID STATE AND SO OUR PACKING MATERIALS, OUR CARDBOARD BOXES, THE PAPER, THE WRAPPING THAT WE HAVE THINGS IN AREN T AFFECTED BECAUSE THERE S NEVER A LIQUID STATE THAT CAUSES THEN THIS TYPE OF DESTRUCTION OF THE WRAPPING MATERIAL. SO IT LOOKS LIKE ICE BUT IT S CALLED DRY ICE BECAUSE IT NEVER HAS A LIQUID STATE. SO CARBON DIOXIDE OR DRY ICE IS USED VERY EXTENSIVELY OF COURSE FOR PACKING MATERIALS FOR COLD FOOD SHIPPING ICE CREAM, SHIPPING FROZEN PRODUCTS ACROSS THE COUNTRY, WHATEVER DRY ICE IS USED FOR THAT MATERIAL. SUBLIMATION THEN. OKAY, ALRIGHT, TOMORROW THEN WE WILL TAKE A FURTHER LOOK AT SOLIDS AND LOOK AT SOME OF THE ENERGY CHANGES INVOLVED IN THEM AS WELL.