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Dr. S. M. Condren Chapter 6 Thermochemistry
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Dr. S. M. Condren Thermite Reaction
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Dr. S. M. Condren Thermite Reaction
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Dr. S. M. Condren Terminology Energy capacity to do work Kinetic Energy energy that something has because it is moving Potential Energy energy that something has because of its position
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Dr. S. M. Condren Kinetic Energy
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Dr. S. M. Condren Chemical Potential Energy
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Dr. S. M. Condren Chemical Potential Energy
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Dr. S. M. Condren Internal Energy The sum of the individual energies of all nanoscale particles (atoms, ions, or molecules) in that sample. E = 1/2mc 2 The total internal energy of a sample of matter depends on temperature, the type of particles, and how many of them there are in the sample.
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Dr. S. M. Condren Energy Units calorie - energy required to heat 1-g of water 1 o C Calorie - unit of food energy; 1 Cal = 1-kcal = 1000-cal Joule - 1-cal = 4.184 J = 1-kg*m 2 /sec 2
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Dr. S. M. Condren Law of Conservation of Energy energy can neither be created nor destroyed the total amount of energy in the universe is a constant energy can be transformed from one form to another
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Dr. S. M. Condren First Law of Thermodynamics the amount of heat transferred into a system plus the amount of work done on the system must result in a corresponding increase of internal energy in the system
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Dr. S. M. Condren Thermochemistry Terminology system => that part of the universe under investigation surroundings => the rest of the universe universe = system + surroundings
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Dr. S. M. Condren Thermodynamic System
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Dr. S. M. Condren Energy Transfer Energy is always transferred from the hotter to the cooler sample Heat – the energy that flows into or out of a system because of a difference in temperature between the thermodynamic system and its surroundings
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Dr. S. M. Condren Thermochemistry Terminology state properties => properties which depend only on the initial and final states => properties which are path independent non-state properties => properties which are path dependent state properties => E non-state properties => q & w
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Dr. S. M. Condren Thermochemistry Terminology exothermic - reaction that gives off energy endothermic - reaction that absorbs energy chemical energy - energy associated with a chemical reaction thermochemistry - the quantitative study of the heat changes accompanying chemical reactions thermodynamics - the study of energy and its transformations
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Dr. S. M. Condren 2 H 2(g) + O 2(g) --> 2 H 2 O (g) + heat and light Energy & Chemistry This can be set up to provide ELECTRIC ENERGY in a. in a fuel cell. Oxidation: 2 H 2 ---> 4 H+ + 4 e- 2 H 2 ---> 4 H+ + 4 e-Reduction: 4 e- + O2 + 2 H 2 O ---> 4 OH- 4 e- + O2 + 2 H 2 O ---> 4 OH-
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Dr. S. M. Condren Energy & Chemistry
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Dr. S. M. Condren Enthalpy heat at constant pressure q p = H = H products - H reactants Exothermic Reaction H = (H products - H reactants ) < 0 H 2 O (l) -----> H 2 O (s) H < 0 Endothermic Reaction H = (H products - H reactants ) > 0 H 2 O (l) -----> H 2 O (g) H > 0
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Dr. S. M. Condren Enthalpy H = E + PV H = E + P V E = H – P V Where text uses U for internal energy
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Dr. S. M. Condren Pressure-Volume Work
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Dr. S. M. Condren First Law of Thermodynamics heat => q internal energy => E internal energy change => E work => w E = q - w (Engineering convention)
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Dr. S. M. Condren Specific Heat the amount of heat necessary to raise the temperature of 1 gram of the substance 1 o C independent of mass substance dependent s.h. Specific Heat of Water = 4.184 J/g o C
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Dr. S. M. Condren Heat q = m * s.h. * t whereq => heat, J m => mass, g s.h. => specific heat, J/g* o C t = change in temperature, o C
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Dr. S. M. Condren Molar Heat Capacity the heat necessary to raise the temperature of one mole of substance by 1 o C substance dependent C
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Dr. S. M. Condren Heat Capacity the heat necessary to raise the temperature 1 o C mass dependent substance dependent C
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Dr. S. M. Condren Heat Capacity C = m X s.h. whereC => heat capacity, J/ o C m => mass, g s.h. => specific heat, J/g o C
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Dr. S. M. Condren Plotted are graphs of heat absorbed versus temperature for two systems. Which system has the larger heat capacity? A, B
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Dr. S. M. Condren Heat Transfer q lost = - q gained (m X s.h. X t) lost = - (m X s.h. X t) gained
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Dr. S. M. Condren EXAMPLE If 100. g of iron at 100.0 o C is placed in 200. g of water at 20.0 o C in an insulated container, what will the temperature, o C, of the iron and water when both are at the same temperature? The specific heat of iron is 0.106 cal/g o C. (100.g*0.106cal/g o C*(T f - 100.) o C) = q lost - q gained = (200.g*1.00cal/g o C*(T f - 20.0) o C) 10.6(T f - 100. o C) = - 200.(T f - 20.0 o C) 10.6T f - 1060 o C = - 200.T f + 4000 o C (10.6 + 200.)T f = (1060 + 4000) o C T f = (5060/211.) o C = 24.0 o C
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Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0 o C to steam at 127.0 o C? q = H ice + H fusion + H water + boil. + steam q = H ice + H fusion + H water + boil. + steam
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Dr. S. M. Condren Heat Transfer
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Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0 o C to steam at 127.0 o C? q = H ice + H fusion + H water + boil. + steam q= (10.0g*2.09J/g o C*((0.0 – (-15.0)) o C)) Mass of the ice specific heat of ice Temperature change {
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Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0 o C to steam at 127.0 o C? q = H ice + H fusion + H water + boil. + steam q= (10.0g*2.09J/g o C*15.0 o C) + (10.0g*333J/g) Mass of ice Heat of fusion Melting of ice occurs at a constant temperature
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Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0 o C to steam at 127.0 o C? q = H ice + H fusion + H water + boil. + steam q= (10.0g*2.09J/g o C*15.0 o C) + (10.0g*333J/g) + (10.0g*4.18J/g o C*((100.0-0.00) o C)) Mass of water Specific heat of liquid water Temperature change of the liquid water
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Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0 o C to steam at 127.0 o C? q = H ice + H fusion + H water + boil. + steam q= (10.0g*2.09J/g o C*15.0 o C) + (10.0g*333J/g) + (10.0g*4.18J/g o C*100.0 o C) + (10.0g*2260J/g) Mass of waterHeat of vaporization Boiling of water occurs at a constant temperature
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Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0 o C to steam at 127.0 o C? q = H ice + H fusion + H water + boil. + steam q= (10.0g*2.09J/g o C*15.0 o C) + (10.0g*333J/g) + (10.0g*4.18J/g o C*100.0 o C) + (10.0g*2260J/g) + (10.0g*2.03J/g o C*((127.0-100.0) o C)) Mass of steam Specific heat of steam Temperature change for the steam
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Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0 o C to steam at 127.0 o C? q = H ice + H fusion + H water + boil. + steam q= (10.0g*2.09J/g o C*15.0 o C) + (10.0g*333J/g) + (10.0g*4.18J/g o C*100.0 o C) + (10.0g*2260J/g) + (10.0g*2.03J/g o C*27.0 o C) q = (314 )J + 3.33X10 3 + 4.18X10 3 + 2.26X10 4 + 548 = 30.96 kJ
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Dr. S. M. Condren Spreadsheet of Previous Problem
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Dr. S. M. Condren Bomb Calorimeter Parr calorimeter
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Dr. S. M. Condren EXAMPLE A 1.000g sample of a particular compound produced 11.0 kJ of heat. The temperature of the calorimeter and 3000 g of water was raised 0.629 o C. How much heat is gained by the calorimeter? heat gained = - heat lost heat calorimeter + heat water = heat reaction heat calorimeter = heat reaction - heat water
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Dr. S. M. Condren EXAMPLE A 1.000g sample of a particular compound produced 11.0 kJ of heat. The temperature of the calorimeter and 3000 g of water was raised 0.629 o C. How much heat is gained by the calorimeter? heat calorimeter = heat reaction - heat water heat = 11.0 kJ - ((3.00kg)(0.629 o C)(4.184kJ/kg o C)) = 3.1 kJ
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Dr. S. M. Condren Example What is the mass of water equivalent of the heat absorbed by the calorimeter? #g = (3.1 kJ/0.629 o C)(1.00kg* o C/4.184kJ) = 6.5 x 10 2 g
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Dr. S. M. Condren Example A 1.000 g sample of ethanol was burned in the sealed bomb calorimeter described above. The temperature of the water rose from 24.284 o C to 26.225 o C. Determine the heat for the reaction. m = (3000 + "647")g H 2 O q = m X s.h. X t = (3647g)(4.184J/g o C)(1.941 o C) = 29.61 kJ
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Dr. S. M. Condren When graphite is burned to yield CO 2, 394 kJ of energy are released per mole of C atoms burned. When C 60 is burned to yield CO 2 approximately 435 kJ of energy is released per mole of carbon atoms burned. Would the buckyball-to-graphite conversion be exothermic or endothermic? exothermic, endothermic
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Dr. S. M. Condren Laws of Thermochemistry 1. The magnitude of is directly proportional to the amount of reactant or product. s --> l H => heat of fusion l --> g H => heat of vaporization
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Dr. S. M. Condren Laws of Thermochemistry 2. H for a reaction is equal in magnitude but opposite in sign to H for the reverse reaction. H 2 O (l) -----> H 2 O (s) H < 0 H 2 O (s) -----> H 2 O (l) H > 0
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Dr. S. M. Condren Laws of Thermochemistry 3. The value of H for the reaction is the same whether it occurs directly or in a series of steps. H overall = H 1 + H 2 + H 3 + · · ·
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Dr. S. M. Condren Hess' Law a relation stating that the heat flow in a reaction which is the sum of a series of reactions is equal to the sum of the heat flows in those reactions
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Dr. S. M. Condren EXAMPLE CH 4(g) + 2 O 2(g) -----> CO 2(g) + 2 H 2 O (l) CH 4(g) -----> C (s) + 2 H 2(g) H 1 2 O 2(g) -----> 2 O 2(g) H 2 C (s) + O 2(g) -----> CO 2(g) H 3 2 H 2(g) + O 2(g) -----> 2 H 2 O (l) H 4 --------------------------------------------- CH 4(g) + 2 O 2(g) -----> CO 2(g) + 2 H 2 O (l) H overall = H 1 + H 2 + H 3 + H 4
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Dr. S. M. Condren Standard Enthalpy of Formation the enthalpy associated with the formation of a substance from its constituent elements under standard state conditions
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Dr. S. M. Condren Calculation of H o H o = c* H f o products - c* H f o reactants
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Dr. S. M. Condren Example What is the value of H rx for the reaction: 2 C 6 H 6(l) + 15 O 2(g) --> 12 CO 2(g) + 6 H 2 O (g) from Appendix J Text C 6 H 6(l) H f o = + 49.0 kJ/mol O 2(g) H f o = 0 CO 2(g) H f o = - 393.5 H 2 O (g) H f o = - 241.8 H rx c* H f o product - c* H f o reactants
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Dr. S. M. Condren Example What is the value of H rx for the reaction: 2 C 6 H 6(l) + 15 O 2(g) --> 12 CO 2(g) + 6 H 2 O (g) from Appendix J Text C 6 H 6(l) H f o = + 49.0 kJ/mol; O 2(g) H f o = 0 CO 2(g) H f o = - 393.5; H 2 O (g) H f o = - 241.8 H rx c* H f o product - c* H f o reactants H rx - 393.5) + 6(- 241.8) product - 2(+ 49.0 ) + 15(0) reactants kJ/mol = - 6.271 x 10 3 kJ
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Dr. S. M. Condren Example What is the value of H rx for the reaction: Fe 2 O 3(s) + 2 Al (s) --> 2 Fe (l) + Al 2 O 3(s) from Appendix J Text Fe 2 O 3(s) H f o = -825.5 kJ/mol; Al (s) H f o = 0 kJ/mol Al 2 O 3(s) H f o = - 1675.7 kJ/mol; Fe (l) H f o = +12.4 kJ/mol H rx c* H f o product - c* H f o reactants H rx - 1675.7) + 2(- 12.4) product - 1(-825.5 ) + 2(0) reactants kJ/mol = - 2.4764 x 10 3 kJ
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Dr. S. M. Condren Thermite Reaction on Saturday ~150g Fe 2 O 3 ~1 mol Fe 2 O 3 ~2.5x10 6 J ~2.5MJ
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Dr. S. M. Condren Fossil Fuels natural gas coal petroleum
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Dr. S. M. Condren Energy Sources
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Dr. S. M. Condren Based on 1998 Data
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