17-1 CHEM 102, Fall 2014 LA TECH Instructor: Dr. Upali Siriwardane Office: CTH 311 Phone Office Hours: M,W 8:00-9:00 & 11:00-12:00 am; Tu,Th,F 9: :30 am. or by appointment. Test Dates : 9:30-10:45 am., CTH 328 Chemistry 102(01) Spring 2014 March 31, 2014 (Test 1): Chapter 13 April 23, 2014 (Test 2): Chapter 14 &15 May 19, 2014 (Test 3) Chapter 16 &17 May 21, 2014 (Make-up test) comprehensive: Chapters 13-17

17-2 CHEM 102, Fall 2014 LA TECH Chapter 6. Thermochemistry 6.1 Chemical Hand Warmers The Nature of Energy: Key Definitions The First Law of Thermodynamics: There Is No Free Lunch Quantifying Heat and Work Measuring for Chemical Reactions: Constant-Volume Calorimetry Enthalpy: The Heat Evolved in a Chemical Reaction at Constant Pressure Constant-Pressure Calorimetry: Measuring Relationships Involving Determining Enthalpies of Reaction from Standard Enthalpies of Formation Energy Use and the Environment 263

17-3 CHEM 102, Fall 2014 LA TECH Chapter 17. Free Energy and Thermodynamics 17.1 Nature’s Heat Tax: You Can’t Win and You Can’t Break Even Spontaneous and Nonspontaneous Processes Entropy and the Second Law of Thermodynamics Heat Transfer and Changes in the Entropy of the Surroundings Gibbs Free Energy Entropy Changes in Chemical Reactions: Calculating Free Energy Changes in Chemical Reactions: Calculating Free Energy Changes for Nonstandard States: The Relationship between and Free Energy and Equilibrium: Relating to the Equilibrium Constant (K)

17-4 CHEM 102, Fall 2014 LA TECH What forms of energy are found in the Universe? mechanicalthermalelectricalnuclear mass: E = mc 2 others yet to discover

17-5 CHEM 102, Fall 2014 LA TECH What is 1 st Law of Thermodynamics Eenergy is conserved in the Universe All forms of energy are inter-convertible and conserved Energy is neither created nor destroyed.

17-6 CHEM 102, Fall 2014 LA TECH What exactly is  H? Heat measured at constant pressure q p Chemical reactions exposed to atmosphere and are held at a constant pressure. Volume of materials or gases produced can change.

17-7 CHEM 102, Fall 2014 LA TECH What is the internal energy change (  U) of a system?  U is part of energy associated with changes in atoms, molecules and subatomic particles  U is part of energy associated with changes in atoms, molecules and subatomic particles E total = E ke + E pe +  U  U = heat (q) + w (work)  U = q + w  U = q -P  V; w =- P  V

17-8 CHEM 102, Fall 2014 LA TECH Heat measured at constant volume q v Chemical reactions take place inside a closed chamber like a bomb calorimeter. Volume of materials or gases produced can not change. ie: work = -P  V= 0  U = q v + w qv =  U + o;w = 0  U = q v =  U(internal energy ) How is Internal Energy,  U measured?

17-9 CHEM 102, Fall 2014 LA TECH Enthalpy Heat changes at constant pressure during chemical reactions Thermochemical equation. eg. H 2 (g) + O 2 (g) ---> 2H 2 O(l)  H =- 256 kJ;  is called the enthalpy of reaction. if  H is + reaction is called endothermic if  H is - reaction is called exothermic

17-10 CHEM 102, Fall 2014 LA TECH The thermodynamic property related to randomness is ENTROPY, S. Product-favored processes: final state is more DISORDERED or RANDOM than the original. Spontaneity is related to an increase in randomness. Reaction of K with water Entropy, S

17-11 CHEM 102, Fall 2014 LA TECH Physical Process” S[H 2 O(l)] > S[H 2 O(s)] at 0  C.

17-12 CHEM 102, Fall 2014 LA TECH   G o =  H o - T  S o  If  H is negative it helps product to be favored  If  S is positive it helps product to be favored  If  G is negative reaction is product favored Gibbs free energy change = difference between the enthalpy of a system and the product of its absolute temperature and entropy predictor of spontaneity Total energy change of the system - energy lost in disordering the system Total energy change of the system - energy lost in disordering the system Gibbs Free Energy, G

17-13 CHEM 102, Fall 2014 LA TECH Thermodynamics Standard States The thermodynamic standard state of a substance is its most stable pure form under standard pressure (1 atm) and at some specific temperature (25 ºC or 298 K) standard pressure (1 atm) and at some specific temperature (25 ºC or 298 K) superscript circle is used to denote a thermodynamic quantity that is under standard state conditions: ΔH = ΔH° ΔS = ΔS° ΔG = ΔG° ΔH = ΔH° ΔS = ΔS° ΔG = ΔG°

17-14 CHEM 102, Fall 2014 LA TECH Hydrogen ΔH o f (kJ/mol) ΔG o f (kJ/mol) S o (J/mol K) H 2 (g) H (g) H 2 O (l) H 2 O (g) H 2 O 2 (l) Standard Thermodynamic Data ΔH o f - Standard Enthalpy of Formation ΔG o f - Standard Free Energy of Formation S o - Standard Free Energy of Formation

17-15 CHEM 102, Fall 2014 LA TECH Standard Molar Entropy Values

17-16 CHEM 102, Fall 2014 LA TECH Chemical Thermodynamics spontaneous reaction – reaction which proceed without external assistance once started chemical thermodynamics helps predict which reactions are spontaneous

17-17 CHEM 102, Fall 2014 LA TECH Will the rearrangement of a system decrease its energy? If yes, system is favored to react — a product-favored system. Most product-favored reactions are exothermic. Often referred to as spontaneous reactions. “Spontaneous” does not imply anything about time for reaction to occur. Kinetic factors are more important for certain reactions. Thermodynamics

17-18 CHEM 102, Fall 2014 LA TECH 1) Give the definitions of the following: a) Enthalpy (H): b) Enthalpy change of a thermo-chemical reaction (  H): c) Entropy of a substance (S): d) Entropy change of a chemical reaction(  S): e) Thermodynamic Standard State( 0 ):

17-19 CHEM 102, Fall 2014 LA TECH Laws of Thermodynamics Zeroth: Thermal equilibrium and temperature First : The total energy of the universe is constant Second : The total entropy (S) of the universe is always increasing Third : The entropy(S) of a pure, perfectly formed crystalline substance at absolute zero is zero Zeroth: Thermal equilibrium and temperature First : The total energy of the universe is constant Second : The total entropy (S) of the universe is always increasing Third : The entropy(S) of a pure, perfectly formed crystalline substance at absolute zero is zero

17-20 CHEM 102, Fall 2014 LA TECH 2) Give the definitions of the following: a) Zero th Law of thermodynamics: b) First Law of thermodynamics: c) Second Law of thermodynamics: d) Third Law of thermodynamics:

17-21 CHEM 102, Fall 2014 LA TECH Why is it necessary to divide Universe into System and Surrounding Universe = System + Surrounding system surroundings universe Boundary?

17-22 CHEM 102, Fall 2014 LA TECH Types of Systems Isolated system no mass or energy exchange Closed system only energy exchange Open system both mass and energy exchange

17-23 CHEM 102, Fall 2014 LA TECH Universe = System + Surrounding Why is it necessary to divide Universe into System and Surrounding

17-24 CHEM 102, Fall 2014 LA TECH 3) Why we need to divide universe into surroundings and system for thermodynamic calculations? Give the signs of the  H (heat) and  S (disorder) and  G ( free energy) when system lose or gain them.  Loss Gain  H (heat)  S (disorder)  G ( free energy)

17-25 CHEM 102, Fall 2014 LA TECH Second Law of Thermodynamics In the universe the ENTROPY cannot decrease for any spontaneous process The entropy of the universe strives for a maximum in any spontaneous process, the entropy of the universe increases for product-favored process  S universe = ( S sys + S surr ) > 0  S univ = entropy of the Universe  S sys = entropy of the System  S surr = entropy of the Surrounding  S univ =  S sys +  S surr

17-26 CHEM 102, Fall 2014 LA TECH Entropy of the Universe  S univ =  S sys +  S surr  s univ  S sys  S surr (  S sys >  S surr) (  S surr >  S sys)

17-27 CHEM 102, Fall 2014 LA TECH 4) Explain the ways that  S of the universe,  S univ could be +.  S univ =  S sys +  S surr + + +

17-28 CHEM 102, Fall 2014 LA TECH Entropy and Dissolving

17-29 CHEM 102, Fall 2014 LA TECH 5) Assign a sign to the entropy change for the following systems. a) mixing aqueous solutions of NaCl and KNO 3 together: b)spreading grass seed on a lawn: c)raking and bagging leaves in the fall: d) d) shuffling a deck of cards: e) raking and burning leaves in the fall:

17-30 CHEM 102, Fall 2014 LA TECH Expansion of a Gas The positional probability is higher when particles are dispersed over a larger volume Matter tends to expand unless it is restricted

17-31 CHEM 102, Fall 2014 LA TECH Gas Expansion and Probability

17-32 CHEM 102, Fall 2014 LA TECH Entropies of Solid, Liquid and Gas Phases S (gases) > S (liquids) > S (solids) S (gases) > S (liquids) > S (solids)

17-33 CHEM 102, Fall 2014 LA TECH 6) Taking following examples explain how disorder is related to a measuring positional probability) or dispersion among the allowed energy states? Expansion of gases: Two gas molecules trapped in two vessels with a tube with a stop cock. a) Expansion of gases: Two gas molecules trapped in two vessels with a tube with a stop cock.

17-34 CHEM 102, Fall 2014 LA TECH. 6) Taking following examples explain how disorder is related to a measuring positional probability) or dispersion among the allowed energy states. Distribution of Kinetic energy at 0, 25 and 100°C for b) Distribution of Kinetic energy at 0, 25 and 100°C for O 2

17-35 CHEM 102, Fall 2014 LA TECH Entropy and Molecular Structure

17-36 CHEM 102, Fall 2014 LA TECH Entropy, S Entropies of ionic solids depend on coulombic attractions. S o (J/Kmol) MgO26.9 NaF51.5 S o (J/Kmol) MgO26.9 NaF51.5

17-37 CHEM 102, Fall 2014 LA TECH Qualitative Guidelines for Entropy Changes Entropies of gases higher than liquids higher than solids Entropies are higher for more complex structures than simpler structures Entropies of ionic solids are inversely related to the strength of ionic forces Entropy increases when making solutions of pure solids or pure liquids in a liquid solvent Entropy decrease when making solutions of gases in a liquid

17-38 CHEM 102, Fall 2014 LA TECH Entropy of a Solution of a Gas

17-39 CHEM 102, Fall 2014 LA TECH 7) Arrange following in the order of increasing entropy? a) C(s) (diamond) b) C(s) (graphite) c) O 2 (g) d) CO 2 (g) e) CO(g) f) Hg(l)

17-40 CHEM 102, Fall 2014 LA TECH Entropy Change Entropy (  S) normally increase (+) for the following changes: i) Solid ---> liquid (melting) + ii) Liquid ---> gas + iii) Solid ----> gas most + iv) Increase in temperature + v) Increasing in pressure(constant volume, and temperature) + vi) Increase in volume +

17-41 CHEM 102, Fall 2014 LA TECH Qualitative prediction of  S of Chemical Reactions Look for (l) or (s) --> (g) Look for (l) or (s) --> (g) If all are gases: calculate  n If all are gases: calculate  n  n =  n (gaseous prod.) -  n(gaseous reac.) N 2 (g) + 3 H 2 (g) > 2 NH 3 (g)  n = = -2 If  n is -  S is negative (decrease in S) If  n is +  S is positive (increase in S)

17-42 CHEM 102, Fall 2014 LA TECH Predict  S! 2 C 2 H 6 (g) + 7 O 2 (g)--> 4 CO 2 (g) + 6H 2 O(g) 2 CO(g) + O 2 (g)-->2 CO 2 (g) 2 CO(g) + O 2 (g)-->2 CO 2 (g) HCl(g) + NH 3 (g)-->NH 4 Cl(s) HCl(g) + NH 3 (g)-->NH 4 Cl(s) H 2 (g) + Br 2 (l) --> 2 HBr(g) H 2 (g) + Br 2 (l) --> 2 HBr(g)

17-43 CHEM 102, Fall 2014 LA TECH 8) Taking following physical and chemical changes qualitatively predict the sign of  S. a) 2H 2 O (g) > 2 H 2 O (l) b) 2H 2 O (g) > 2 H 2 (g) + O 2 (g) c) N 2 (g) + 3 H 2 (g) > 2 NH 3 (g)

17-44 CHEM 102, Fall 2014 LA TECH Entropy Changes for Phase Changes For a phase change,  S SYS = q SYS /T (q = heat transferred) Boiling Water H 2 O (liq)  H 2 O(g)  H = q = +40,700 J/mol

17-45 CHEM 102, Fall 2014 LA TECH 9) How is entropy related to the heat and temperature?

17-46 CHEM 102, Fall 2014 LA TECH Phase Transitions Heat of Fusion energy associated with phase transition solid-to- liquid or liquid-to-solid  G fusion = 0 =  H fusion - T  S fusion 0 =  H fusion - T  S fusion  H fusion = T  S fusion Heat of Vaporization energy associated with phase transition gas-to- liquid or liquid-to-gas  H vaporization = T  S vaporization

17-47 CHEM 102, Fall 2014 LA TECH 10) The normal boiling point of benzene is 80.1°C and heat of evaporation (∆H°vap)is 30.7 kJ/mol. Calculate the ∆S surr (in J/K mol) for the evaporation of benzene.

17-48 CHEM 102, Fall 2014 LA TECH Can calc. that H o rxn = H o system = kJ Can calc. that  H o rxn =  H o system = kJ 2 H 2 (g) + O 2 (g)  2 H 2 O(liq)  S o sys = J/K Entropy Changes in the Surroundings = J/K 2nd Law of Thermodynamics

17-49 CHEM 102, Fall 2014 LA TECH 2 H 2 (g) + O 2 (g)  2 H 2 O(liq)  S o sys = J/K  S o surr = J/K  S o uni = J/K The entropy of the universe is increasing, so the reaction is product-favored. 2nd Law of Thermodynamics

17-50 CHEM 102, Fall 2014 LA TECH Gibbs Free Energy, G  S univ =  S surr +  S sys Multiply through by (-T) -T  S univ =  H sys - T  S sys -T  S univ =  G system Under standard conditions —  G o =  H o - T  S o  S univ =  H sys T +  S

17-51 CHEM 102, Fall 2014 LA TECH Gibbs Free Energy, G   G o =  H o - T  S o Gibbs free energy change = difference between the enthalpy of a system and the product of its absolute temperature and entropy predictor of spontaneity Total energy change for system - energy lost in disordering the system Total energy change for system - energy lost in disordering the system

17-52 CHEM 102, Fall 2014 LA TECH 11) Define the following: Gibbs Free Energy (G): a) Gibbs Free Energy (G): Gibbs Free Energy change for a reaction (  G): b) Gibbs Free Energy change for a reaction (  G): How is  G sys is related to  S uni and temperature? c) How is  G sys is related to  S uni and temperature?

17-53 CHEM 102, Fall 2014 LA TECH  G The sign of  G indicates whether a reaction will occur spontaneously. +Not spontaneous 0 At equilibrium -Spontaneous  S  G The fact that the effect of  S will vary as a function of temperature is important. This can result in changing the sign of  G. Free energy,  G

17-54 CHEM 102, Fall 2014 LA TECH  G The sign of  G indicates whether a reaction will occur spontaneously. Therefore E cell value have to be + (positive) for spontaneous redox reaction  G = -nFE cell  G = -nFE cell n = number of electrons transferred F = Faraday constant ((96500 C/mol) E cell = E ½ (cathode)- E ½ (anode)  G and E cell

17-55 CHEM 102, Fall 2014 LA TECH How do you calculate  G at different T and P  G =  G o + RT ln Q Q = reaction quotient Q = reaction quotient at equilibrium  G =   =  G o + RT ln K  G o = - RT ln K If you know  G o you could calculate K or vice versa.   G = -nFE c ell Nerst Equation, since   G = -nFE c ell

17-56 CHEM 102, Fall 2014 LA TECH 11) Define the following: How you decided from the sign of  G whether and chemical reaction is? d) How you decided from the sign of  G whether and chemical reaction is? i) Spontaneousii) Never take place iii) Equilibrium How is Gibbs Free Energy change (  G°) related to E cell : e) How is Gibbs Free Energy change (  G°) related to E cell : How is non standard (  G) related to (  G ° ) and Q (reaction quotient) f) How is non standard (  G) related to (  G ° ) and Q (reaction quotient)

17-57 CHEM 102, Fall 2014 LA TECH 11) Define the following: How is standard (  G ° ) related to K eq (equilibrium constant)? g) How is standard (  G ° ) related to K eq (equilibrium constant)?

17-58 CHEM 102, Fall 2014 LA TECH Gibbs Free Energy, G  G o =  H o - T  S o  G o =  H o - T  S o  H o  S o  G o Reaction exo(-)increase(+)-Prod-favored endo(+)decrease(-)+React-favored exo(-)decrease(-)?T dependent endo(+)increase(+)?T dependent

17-59 CHEM 102, Fall 2014 LA TECH 12) Predict the  G sys changes for different signs of  H sys and  S sys at low/high temperatures for the equation:  G sys =  H sys -T  S sys  G sys  H sys  T  S sys a) b) c) d)