Pre-AP Chemistry Basic Thermochemistry Equilibrium and Organic Chemistry Notes Unit 112
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Transcript of Pre-AP Chemistry Basic Thermochemistry Equilibrium and Organic Chemistry Notes Unit 112
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¬&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¬&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¬&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¬&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&ofðanol&(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&ofðanol&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¬&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?&
&