Unit%11:%Basic%Thermochemistry,%Equilibrium,%and%Organic%Chemistry%

Pre>AP%Chemistry%%%

Mr.%Patel%

SWHS%

Topic&Outline&•  MUST&have&a&scien1fic&calculator&(not&graphing)!!%•  Energy&and&Enthalpy&(17.1,&17.2)&•  Thermochemical&Equa1ons&(17.2)&•  Calorimetry&(17.2)&•  Hess’s&Law&(17.4)&•  Enthalpy&of&State&Change&(17.3)&•  Collision&Theory/Reac1on&Rate&(18.1)&•  Chemical&Equilibrium&(18.2)&•  Law&of&Mass&Ac1on&(18.2)&•  Organic&Chemistry&(22.1,&22.2,&22.4)&&

&

PART%I:%THERMOCHEMISTRY%

Energy&

•  Thermochemistry&–&study&of&energy&changes&in&chemical&reac1ons&and&changes&of&state&– Energy&is&not&maRer&– Poten1al&Energy&in&bonds&

•  Energy&changes&are&a&result&of&heat&transfer&and/or&work&

•  Heat&–&energy&–&symbolizes&as&q"

Energy&•  Law&of&Conserva1on&of&Energy&–  Energy&is&neither&created&nor&destroyed;&only&transferred&&

•  Reference&points&–  System&–&focused&reac1on&–  Surrounding&–&everything&other&than&the&system&– Universe&=&System&+&Surrounding&

Heat&Transfer&•  Heat&flow&is&in&terms&of&the&system&in&chemistry&

•  Endothermic&–&system&absorbs&heat&– Posi1ve&q"

•  Exothermic&–&system&releases&heat&– Nega1ve&q"

•  Heat&flows&from&warmer&to&cooler&objects&

Heat&Flow&

•  Units:&calorie&(cal)&or&joule&(J)&&–  1000&calories&=&1&Calorie&(food)&–  “10g&sugar&has&41&Calories”&

•  When&10g&of&sugar&consumed,&41000&calories&of&heat&produced&

–  SI&unit&of&energy&is&joule&&•  This&is&the&unit&that&will&be&used&in&class&

•  The&more&heat&an&object&gains,&the&hoRer&it&gets&– All&substances&change&temp&when&heated&but&the&magnitude&of&the&temp&change&depends&on&the&substance&

Heat&Capacity&(C)&

•  The&amount&of&energy&needed&to&raise&the&temperature&of&an&object&by&1.00oC&

•  This&quan1ty&depends&on&mass&– Extensive&property&– The&greater&the&mass,&the&greater&the&heat&capacity"

•  Units:&J/oC&•  Equa1on:"""""""q&=&C&x&∆T&&&&&&&∆&=&change&(final&–&ini1al)"

Specific&Heat&(c&or&S)&•  The&amount&of&energy&needed&to&raise&the&temperature&of&1.00%g%of&an&object&by&1.00oC&

•  This&quan1ty&does&not&depend&on&mass&–  Intensive&property&–  The&greater&the&specific&heat,&the&greater&the&heat&required&to&raise&the&temperature&

–  If&it&takes&a&lot&of&heat&to&raise&the&temperature,&it&will&release&a&lot&of&heat&as&is&cools&&

– Memorize&specific&heat&of&water:&4.184&J/goC&•  Units:&J/(goC)&&•  Equa1on:"""""""""""""q&=&m&x&S&x&∆T&&&&&&&∆&=&change&(final&–&ini1al)"

Ex:&The&temperature&of&a&3.40g&of&a&substance&increases&from&21oC&to&85oC.&How&much&heat&is&absorbed&if&the&specific&heat&is&2.00&J/(goC)?&

Ex:&How&many&kilojoules&of&heat&does&32.0g&of&water&absorb&when&it&is&heated&from&25.0oC&to&80.0oC.&Water&has&a&very&high&specific&heat:&4.184&J/(goC).&

Ex:&Calculate&the&specific&heat&of&25.0g&of&copper&if&it&takes&487.5&J&to&heat&it&from&25.0oC&to&75.0oC.&

Enthalpy&(H)&

•  The&heat&content&of&a&system&at&constant"pressure&is&called&enthalpy&(symbol:&H)&

•  Typically&we&do&not&focus&on&the&actual&enthalpy&– Focus&more&on&the&change&in&enthalpy&∆H&– Heat&and&enthalpy&change&used&interchangeably&– q&=&∆H&

•  Enthalpy&is&a&state&func1on&–&path&does&not&maRer;&only&ini1al&and&final&states&

State&Func1on&

Thermochemical&Equa1ons&•  A&chemical&equa1on&can&convey&informa1on&about&heat&transfer&

(enthalpy&change)&–&treat&heat&as&reactant&or&product&–  Important&to&indicate&the&physical&state&of&the&chemicals&–  The&reverse&of&a&reac1on&has&the&same&magnitude&of&∆H&but&opposite&sign&

•  Endothermic&reac1on&(+∆H)&–  &2&NaHCO3&&!&&Na2CO3&+&&H2O&&+&CO2&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&∆H&=&129&kJ&–  &2&NaHCO3&&+&&129%kJ%%!&&Na2CO3&+&&H2O&&+&CO2&&

•  Exothermic&reac1on&(–∆H)&–  CaO&+&H2O&!&Ca(OH)2&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&∆H&=&–&65.2&kJ&–  CaO&+&H2O&!&Ca(OH)2&&+&&65.2%kJ%%

•  The&enthalpy&change&can&be&treated&as&part&of&the&mole&ra1o&(stoichiometry!!!)&

Ex:&The&synthesis&of&carbon&disulfide&is&an&endothermic&process&absorbing&89.3&kJ&of&heat.&Calculate&the&amount&

of&heat&(kJ)&absorbed&when&5.66g&of&CS2&is&formed.&C&&+&&2S&&!&&CS2&

Ex:&The&combus1on&of&ethanol&(C2H5OH)&is&an&exothermic&process&releasing&1368&kJ&of&heat.&(a)&Provide&the&thermochemical&

equa1on&for&this&reac1on.&(b)&How&much&heat&is&released&when&12.5g&of&ethanol&combusts?&

&

First&Law&of&Thermodynamics&

•  Total&energy&of&the&universe&is&constant&– There&is&no&change&in&the&heat&in&the&universe&– qsys""+""qsurr"=&0&–  "qsys""=&–&qsurr"&

•  If&system&releases&heat,&surrounding&absorbs&heat&and&vice&versa&–  If&sys&becomes&cooler,&surr&becomes&warmer&

Ex:&A&container&holding&150.0g&of&water&is&at&80.0oC.&What&volume&of&water&(22oC)&must&be&added&to&the&container&to&achieve&a&final&

temperature&of&55.0oC&given&SH2O&=&4.184&J/(goC)?&&&

Ex:&A&50.0g&block&of&iron&is&placed&into&475&g&of&water&at&45.0oC.&At&thermal&equilibrium,&the&temperature&was&62.5oC.&Determine&the&ini1al&temperature&of&the&iron&block&given&SH2O&=&4.184&J/(goC)&and&

SFe&=&0.4495&J/(goC).&&&

Calorimetry&

•  Enthalpy&change&can&be&measured&experimentally&at&constant&pressure&

•  Calorimetry&–&measurement&of&heat&flow&in&chemical&and&physical&processes&– Measured&by&a&device&called&a&calorimeter&– Heat&absorbed&by&system&is&equal&in&magnitude&to&the&heat&released&by&the&surrounding&

–  Two&Types:&Constant&Pressure&and&Constant&Volume&

ConstantmPressure&Calorimetry&

•  For&many&reac1ons&that&occur&in&solu1on,&it&is&easy&to&control&the&pressure…easy&to&find&∆H&– heat&at&constant&pressure&is&∆H&

•  A&simple&constantmP&calorimeter&can&be&made&using&foam&cups&–&liRle&heat&loss&– Called&“coffee&cup”&calorimeter&– Not&sealed&so&remains&at&constant&pressure&

CoffeemCup&Calorimeter&

ConstantmPressure&Calorimetry&•  Reactants&dissolved&in&water;&reac1on&occurs&in&aqueous&solu1on&–  Reactant/Products&–&reac1on&=&system&–  Solvent&=&surrounding&– No&physical&separa1on&between&system&and&surrounding&&

– Heat&produced&by&the&reac1on&(system)&is&absorbed&by&the&solvent&(surrounding)&

–  qsys&=&–qsurr&&&&&&&&&&&&&&or&&&&&&&&&&&&qrxn%=%–qsoln%%–  To&determine&the&∆H&of&the&reac1on,&you&need&to&know&the&temperature&change&of&the&solu1on,&mass&of&solu1on&(density),&and&the&specific&heat&

–  +qrxn&=&endothermic&&&&&&&&&&&&&–qrxn&=&exothermic&&

Ex:&Calculate&∆H&(kJ)&when&50.00&mL&of&AgNO3&and&50.00&mL&of&HCl&are&mixed&in&a&coffeemcup&calorimeter.&The&temperature&of&the&mixture&increases&from&22.30oC&to&23.11oC.&The&solu1on&has&a&

specific&heat&of&4.184&J/(goC)&and&density&of&1.00&g/mL.&&&

Ex:&A&sample&of&aluminum&at&100oC&is&placed&in&250.0&mL&of&water&at&22oC:&constantmpressure&calorimetry.&At&thermal&equilibrium,&the&

temperature&is&25.2oC.&What&is&the&mass&of&the&Al&given&&SH2O&=&4.184&J/(goC)&and&Sal&=&0.90&J/(goC)?&&

&

ConstantmVolume&Calorimetry&•  Combus1on&reac1ons&are&studied&using&constantmvolume&

calorimetry&–  Called&Bomb&Calorimetry&–  Substance&placed&in&a&sealed,&pressurized&(O2)&vessel&called&a&bomb&

–  Bomb&is&immersed&in&water&in&a&calorimeter&•  Combus1on&releases&heat&

–  Causes&a&temperature&change&in&water&–  Causes&temperature&change&in&calorimeter&(can&not&be&ignored)&–  Reactant/Products&–&reac1on&=&system&–  Solvent&+&calorimeter&=&surrounding&–  qsys&=&–qsurr&&&&&&&&&&&&&&or&&&&&&&&&&&&qrxn%=%–%(qwater%+%qcalorimeter)%–  Note:&water&has&specific&heat;&calorimeter&has&heat&capacity&&

Bomb&Calorimeter&

Ex:&A&hydrocarbon&(80.00g)&is&combusted&in&a&bomb&calorimeter.&The&bomb&is&immersed&in&1.00&kg&water.&The&temperature&of&the&calorimetry&and&its&contents&increased&from&25.0oC&to&46.3oC.&&(a)&Calculate&∆H&for&the&system&given&SH2O&=&4.184&J/(goC)&and&&

Ccal&=&2.00&J/oC.&(b)&If&the&molar&mass&of&the&compound&is&40.00g/mol,&what&is&the&enthalpy&change&in&kJ/mol?&

&