CHM 111 Dr. Kevin Moore

CHM 111 Dr. Kevin Moore

Kinetic Energy Energy of motion E k 1 2 mv 2 Potential Energy Energy of position (stored)

Law of Conservation of Energy Energy cannot be created or destroyed; it can only be converted into different forms Forms of Energy

Energy of the motion of atoms Temperature Measure of the heat content of a system Heat Amount of energy transferred between two bodies as a result of the difference in Temperature between them

Calorie amount of heat required to raise 1g of water from 14.5 to 15.5 C Food calorie is really 1 kcal Joule SI Unit of heat Energy required to supply 1 watt for 1 second 1 cal = 4.184 J

Energy stored in the bonds of a compound Exothermic reactions release stored energy 1 st Law of Thermodynamics Total Energy of an Isolated System is a Constant Restatement of the Law of Conservation of Energy E sys E 0 surr

Function whose final value is independent of the path taken Official Definition: Function or property whose value depends solely on the present state or condition of the system Internal Energy (ΔE) is a state function Temperature Volume

E E E f i Energy Leaves a System: Negative (-) E i > E f Energy Enters a System: Positive (+) E i < E f

CH ( g) 2O ( g) CO ( g) 2H O( g) 802 kj 4 2 2 2 802 kj of energy produced in the reaction Energy released (negative) ΔE=-802kJ

Work force applied which creates movement of an object w F d Work is done by volume expansion in most chemical systems Shown by the difference in the # moles of gas

Initial Final Change

Compare moles of product gas to moles of reactant gas w P V CH( g) 5O( g) 3CO ( g) 4HOg ( ) 3 8 2 2 2 System expands from 6 moles of gas to 7 moles of gas 1 mole of gas takes up 22.4 L under normal conditions

Volume Expansion (sign) V V V f i If Volume changes from 5.0 L to 10.0 L V 10. 0 L 50. L 50. L

Consider a system with an external pressure of 5.0 atm. How much work was done if it expanded from 12.0L to 14.5 L? w 50. atm 25. L 125. Latm 101 J 12. 5 Latm 1300 J 13. 1 L atm kj

Energy is work (w) + heat (q) E q w E q PV q E P V

Two conditions under which a chemical reaction can occur Constant Volume (q v ) qv E P V q E Constant Pressure (q p ) v qp E P V q H E PV p

ΔH Enthalpy Change State Function H H H final initial H H H products reac tan ts

CH( g) 5O( g) 3CO ( g) 4HOg ( ) E 3 8 2 2 2 2045 kj H 2043 kj Difference between ΔH & ΔE is very small w=2 kj Comes from the expansion of 6 moles to 7 moles

CH ( g) 2O ( g) CO ( g) 2H O( g) H E 802 kj 4 2 2 2 For constant pressure calculations Enthalpy = Total Energy if no mole change\ Thermodynamic Standard State 25 C, 1 atm, 1M for solutions Most stable form of a substance under standard conditions

Heat of Fusion (Enthalpy of Fusion - ΔH fus ) Amount of heat necessary to convert 1 mole of a solid substance to liquid without changing its T Heat of Vaporization (ΔH vap ) Amount of heat necessary to convert 1 mole of a liquid substance to gas without changing its T Heat of Sublimation (ΔH sub ) Amount of heat necessary to convert 1 mole of a solid substance to vapor without changing its T Always equals the sum of ΔH vap & ΔH fus

How much heat is needed to melt 5.0 g of H 2 O(ice)? ΔH fus = 6.01 kj/mol 1 mol 50. g 028. mol H2O 18. 02 g 028. mol 601. kj 1 mol 17. kj

Endothermic Energy taken in Cold Reaction Exothermic Energy released Hot Reaction 2Al() s Fe O () s Al O () s 2Fe() s H 852 kj 2 3 2 3 Reversing a reaction reverses the sign of ΔH 2Fe() s Al O () s Fe O () s 2Al() s H 852 kj 2 3 2 3

Calculate the amount of heat released by 5.00 g of Aluminum Predicting Heat Calculate moles of substance Create a mole ratio using kj For Aluminum: 852 kj 2 mol Al 500. g 1 mol Al 26. 98 g 2 852 kj 788. mol Al kj

How much heat is released when 15.5 g of propane is combusted? CH( g) 5O ( g) 3CO ( g) 4HOl ( ) H 2219 kj 3 8 2 2 2 155. g 1 mol C H 441. g 3 8 2219 kj 1 mol C H 3 8 780. kj

How much heat is produced by the combustion of 100.0 g of Nitromethane? 4CH NO ( l) 7O ( g) 4NO ( g) 4CO ( g) 6H O( g) H 24416. kj 3 2 2 2 2 2 100. 0g 1 mol CH NO 6105. g 3 2 4 24416. kj mol CH NO 3 2 999. 8 kj

Calculations of the Enthalpy of a reaction (ΔH) from Temperature changes Calorimeter Insulated Device used to measure temperature changes caused by a reaction Bomb Calorimeter Device used to measure total Energy of a combustion reaction

Bomb is submerged in an insulated water bath Temperature change of water is measured

Specific Heat Capacity Amount of Heat required to raise 1 g of a substance by 1 C Molar Heat Capacity Amount of Heat required to raise 1 mole of a substance by 1 C

Substance Specific Heat (J/g C) Molar Heat Capacity Aluminum 0.902 29.1 Copper 0.385 24.4 Iron 0.450 25.1 Gold 0.129 25.4 Ice 2.03 36.6 Water 4.18 75.3 Mercury 0.140 28.0

q C m T q= Heat C = Specific Heat Capacity m= Mass ΔT= Temperature Change

What is the specific heat of silicon if it takes 192 J to raise 10.0 g by 27.4 C? C 192 J 10. 0g27. 4 C 0. 701 J gc

A 50.0 g sample of Copper at 100.0 C is dropped into 100.0 g of water at 22.5 C. What is the final Temperature? q Cu q H O C m T C m T Cu Cu Cu HO HO HO T ( Cu) T ( H O) f 2 f 2 2 2 2

( 0. 385 ) ( 50. 0 g)( T 100. 0 C) ( 4184. ) ( 100. 0 g) ( T 22. 5 C) J gc f J gc 19. 25( T 100. 0C) 418. 4( T 22. 5 C) f 19. 25T 1925 418. 4T 9414 f f f f 437. 7T 11340 f T f 11340 259. 437. 7 C

A certain mass of ice at 0.00 C is dropped into 50.0 g of water at 55.0 C. If the final temperature is 15.6 C, how much ice was used? (ΔH fus =6.01kJ/mol; C H2O =4.184 J/g C) q q ice ice q 2 H fus H O m 18. 02 q C g q HO HO HO 2 2 2 8240 C ice g mol HO ice 50. 0 156. 550. J 2 m 156. 0. 00 334m 65. 3m 8240 J 8240 m 20. 6 g 399. 3

Enthalpy change for a reaction is the sum of the Enthalpy change of the steps in a reaction. 3H ( g) N ( g) 2NH ( g) 2 2 3 2H ( g) N ( g) N H ( g) H 954. kj 2 2 2 4 N H ( g) H ( g) 2 NH ( g) H 187. 6 kj 2 4 2 3 3H ( g) N ( g) 2NH ( g) H 922. kj 2 2 3

HOl () SO( g) HSO() l H kj 2 2 2 3 62 Ss () O2( g) SO2( g) H 297 kj 1 Ss ( ) HOl ( ) HSg ( ) 2 O2 ( g) H 155 kj 2 2 3 Find ΔH for: HSO( l) HSg ( ) O( g) 2 3 2 2 2

HSO() l HOl () SO( g) H kj 2 3 2 2 62 SO2( g) S ( s) O2( g) H 297 kj 1 Ss ( ) HOl ( ) HSg ( ) 2 O2 ( g) H 155 kj 2 2 ΔH=+514 kj

The Enthalpy Change (ΔH f ) for the formation of 1 mole of a substance from its elements in their standard states. Cs ( ) 2H( g) CH ( g) H 748. kj 2 4 f 1 H2 ( g) 2 O2( g) H2O( g) H f 2418. kj 1 2Cs () 3H ( g) O( g) CHOl () H 277. 7 kj 2 2 2 2 6 f

Heats of formation can be used to calculate the standard Enthalpy of any reaction H n H n H f f products reac tan ts Heat of formation of any element in its standard state is 0

Calculate the Enthalpy of reaction: CaCO () s CaO() s CO ( g) 3 2 H H H f f f ( CaCO ) 1206. 9 ( CaO) 6351. ( CO ) 3935. 2 3 kj mol kj mol kj mol H 1mol 6351. kj 3935. kj 1206. 9 1mol 1mol mol mol mol kj 178. 3 kj

Calculate the ΔH for the following reaction: 4NH ( g) 5O ( g) 4NO( g) 6H O( g) 3 2 2 H H H H f f f f [ NH ] 461. [ O ] 2 3 [ NO] 90. 2 kj mol kj mol [ H O( g)] 2418. 2 0 kj mol H 4mol( 461. ) 184. 4 kj H 4mol( 90. 2 ) 6mol( 2418. ) H react prod prod 1090 kj kj mol kj mol kj mol H Hprod Hreact H 1090kJ ( 184. 4 kj) 905. 6 kj

Heat of Combustion Amount of Heat produced by the combustion of 1 mole of a substance Fuel kj/mol kj/g kj/ml H 2-285.8-141.8-9.9 C 2 H 5 OH -1367-29.7-23.4 C -393.5-32.8-73.8 CH 4-890.3-55.5-30.8 CH 3 OH -726.4-22.7-17.9 C 8 H 18-5470 -47.9-33.6 C 7 H 8-3910 -42.3-36.7

Must be 1 mole Standard Heats are all known CHOHl ( ) 3O ( g) 2CO( g) 3HOl ( ) H 1367 kj 2 5 2 2 2 25 CH ( l) O( g) 8CO ( g) 9HOg ( ) H 5470 kj 8 18 2 2 2 2 Don t need balanced reaction if the Heat of Combustion is known

How much heat is produced in the combustion of 100. g of Toluene (C 7 H 8 ) (ΔH Tol = -3910 kj/mol)? 100. gc H 7 8 1 mol 9215. g 3910 kj 4240 1 mol kj

Blood Sugar (C 6 H 12 O 6 ) C H O aq) 6O ( g) 6CO ( g) H O( l) H 2803 6 12 6( 2 2 2 kj Fat Metabolism 163 C57H110O6 ( s) O2 ( g) 57CO2( g) 55H 2O( l) H 37760 2 kj

Spontaneous Process Process which continues indefinitely once it has been initiated Non-spontaneous Process Process which only happens if an external source of energy continuously influences it Every reaction has a spontaneous direction and its reverse reaction is non-spontaneous An equilibrium state exists

Spontaneous Reactions tend to be exothermic There are spontaneous endothermic reactions Ice Melting/Water Boiling Cold Pack Reactions Entropy (ΔS) Measure of disorder (randomness) in a system 2 nd Law of Thermodynamics An isolated system will increase in Entropy

Entropy increases: Pure becomes dirty (more disorganized) Usually Solid Melts Liquid has higher entropy than the ordered solid Liquid Boils Gas is the highest state of entropy Every atom or molecule is free from all others Reaction creates more moles of gas

Exothermic Process tends to be spontaneous Spontaneous systems tend to increase entropy G H T S ΔG < 0 spontaneous ΔG > 0 non-spontaneous ΔG = 0 - equilibrium

Determine whether an ice cube will melt at 10 C. (ΔH fus =6.01 kj/mol; ΔS fus =22.0 J/Kmol) G H T S G G 6. 01 ( 283 K)( 0. 0220 ) kj mol kj Kmol 601. 623. 022. 220 kj mol kj mol kj mol J mol

At equilibrium, ΔG=0 T H S

Equilibrium occurs at the phase changes If Chloroform has a ΔH vap =29.2 kj/mol and ΔS vap =87.3 J/K-mol. What is its Boiling Point? H 29. 2 T S 0. 0873 T 334 K 61 C kj mol kj K mol

ΔH ΔS At 0 K At High T + + Non-spont Spont + - Non-spont Never Spont - - Spont Non-spont - + Spont Always Spont