Chemical Principles II
Chemical Principles II CHEM 112
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This 0 page Class Notes was uploaded by Herta Weber on Sunday November 1, 2015. The Class Notes belongs to CHEM 112 at Pennsylvania State University taught by Staff in Fall. Since its upload, it has received 13 views. For similar materials see /class/233157/chem-112-pennsylvania-state-university in Chemistry at Pennsylvania State University.
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Date Created: 11/01/15
THERMODYNAMICS Review of Energy and Enthalpy Changes Ch 5 Energy Changes Heat and Work Heat q energy transferred due to a difference in temperature q means heat is added to the system Work w action of force through a distance often PAV w means work is done on the system Energy Changes AE Efinal state Einitial state AE kJmol 02 g gt 2 O atoms 4983 Si s 02 g gt Sio2 s 908 Bojan Chem 112 STATE FUNCTIONS A state function is a quantity that does not depend on the process by which the system was prepared Example Your altitude height above sea level does not depend on the route you took to class this morning State functions are written as uppercase letters E H P V T S Changes in state functions are pathindependent q and w are not state functions but AE q w is a state function Bojan Chem 112 THERMOCHEMISTRY LAWS OF THERMODYNAMICS 1st Law The total energy in the universe is constant AEuniverse O AEuniverse A Esystem A Esurroundings AEsystem A Esurroundings Heat and work AEsystem q w and for PV work at const pressure AE q PAV system Bojan Chem 112 Enthalpy H AH heat transferred at const P H endothermic need to add heat If H exothermic heat is given off Classify as endo or exothermic Ice melting Water boiling Wood burning H is a state function changes are path independent H E PV sums and products of state functions are also state functions Bojan Chem 112 Standard Enthalpy of Formation AH f AH for making a compound from elements in their standard states Standard state is the most stable form pure solid pure liquid or gas at P 1 atm For solutes in solution standard state is usually1M There are tables of AHquotf AH 2 AH f products 2 AH f reactants er39I Bojan Chem 112 SPONTANEOUS REACTIONS A spontaneous reaction How are reaction rate and spontaneity related Examples CH49 2 029 9 3029 2 H20g 2 Fe203s gt4 Fes 3 029 Bojan Chem 112 SPONTANEITY AND WORK Is this process spontaneous Can this process do work What is the reverse of this process Is the reverse process spontaneous Which process can do work 2H202 gt2H20 2H20 gt2H202 Bojan Chem 112 Spontaneity and Equilibrium Spontaneous for T gt 0 C Spontaneous for T lt 0 C H20I gt H20s At 10 C Is it Spontaneous At 10 C Is it Spontaneous At 0 C Bojan Chem 112 Can we predict the spontaneity of a reaction H20I a H20s At 10 c AH lt o 2NaCIs a 2Nas CI2g A H gt o 4Fes 3029 a 2 Fe203s A H lt 0 N2g a 2N J A H gt 0 2H2g 029 6 2H2Og A H lt 0 HYPOTHESIS If AH is negative a reaction will be spontaneous Test this hypothesis Demonstrations BaOH28H20s 2NH4SCNs gt BaSCN2aq 2NH3aq 10H20l At room temperature 20 C H20s gt H20l A H NH4CIs H20l gt NH4CIaq A H SPONTANEITY AH alone doesn t determine spontaneity Another factor RANDOMNESS also determines spontaneity Nature tends to move spontaneously from a state of lower probability to one of higher probability GN Lewis Nobel Laureate Bojan Chem 112 ENTROPY A thermodynamic parameter S that is a measure of the disorder or randomness in a system The more disordered a system the greater its entropy Entropy is a state function AS 3 final 3 initial The Second Law of Thermodynamics For spontaneous processes AS gt0 ASuniv Assystem ASsurrounding gt 0 Bojan Chem 112 ENTROPY Which reactions have AS gt 0 Packaged deck of cards gt Cards spread out on a table Unassembled car parts gt Assembled car CO2 H20 Minerals gt Tree Bojan Chem 112 ENTROPY 1 moles of gas in gt 1 mole of gas in a a 1 liter flask 2 liter flask a b Copyright 2009 Pearson Prentice Hall lnc NH4CIs gt NH4aq Claq Copyright 2009 Pearson Prentice Hall Inc Bojan Chem 112 LAWS OF THERMODYNAMICS 1st Law The total energy in the universe is constant AEuniverse O AEsystem AE AE surroundings universe surroundings AE system 2nd Law The total entropy in the universe is increasing A Suniverse gt 0 A Suniverse A8 AS gt 0 system surroundings 3rd Law The entropy of every pure substance at OK absolute zero temperature is zero SOatOK Bojan Chem 112 3rd LAW of THERMO Entropy is a state function its value depends only on the system39s initial and final states Absolute Entropy S 0 at T 0 K Third Law This means we can measure absolute entropy S Bojan Chem 112 not just AS Increasing temperature Copyright 2009 Pearson Prentice Hall Inc l K i l 39 O 39 l i l 0 ma Molecular Basis of Entropy Solid Liquid Gas Boiling Absolute entropy S Melting O 0 Temperature K gt 1 Adding heat increases entropy S1 mole N2g S1 mole N2g at 300K at 200K Aus at 298K gt Aus at 1000K Molecular Basis of Entropy 2 Entropy depends on the state Solid Liquid Gas 2 e g Boiling g a 4 lt1 Melting 00 Temperature K gt EXAMPLES sol a gas sol a liq liq a gas AS gas a liq gas a sol liq a sol AS AS or l H20 I 25 C gt H209 CaCO3 s gt Ca0s C029 Agaq C aq gt AQCKS Bojan Chem 112