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Chapter 6. Principles of Reactivity: Energy and Chemical Reactions. Thermite Reaction. 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 or its chemical bonding.
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Chapter 6 Principles of Reactivity: Energy and Chemical Reactions Dr. S. M. Condren
Thermite Reaction 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 or its chemical bonding Dr. S. M. Condren
Kinetic Energy Dr. S. M. Condren
Chemical Potential Energy Dr. S. M. Condren
Chemical Potential Energy Dr. S. M. Condren
Internal Energy • The sum of the individual energies of all nanoscale particles (atoms, ions, or molecules) in that sample. • E = 1/2mc2 • 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. Dr. S. M. Condren
Energy Units • calorie - energy required to heat 1-g of water 1oC • Calorie - unit of food energy; • 1 Cal = 1-kcal = 1000-cal • Joule - 1-cal = 4.184 J = 1-kg*m2/sec2 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 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 Dr. S. M. Condren
Thermochemistry Terminology system => that part of the universe under investigation surroundings => the rest of the universe universe = system + surroundings Dr. S. M. Condren
System and Surroundings • SYSTEM • The object under study • SURROUNDINGS • Everything outside the system Dr. S. M. Condren
Announcement Learn@UW will be unavailable on Thursday July 19 from 5:00am until 12:00 noon. Dr. S. M. Condren
Energy & Chemistry 2 H2(g) + O2(g) --> 2 H2O(g) + heat and light This can be set up to provide ELECTRIC ENERGY in a fuel cell. Oxidation: 2 H2 ---> 4 H+ + 4 e- Reduction: 4 e- + O2 + 2 H2O ---> 4 OH- H2/O2 Fuel Cell Energy, page 288 Dr. S. M. Condren
Energy & Chemistry ENERGY is the capacity to do work or transfer heat. HEAT is the form of energy that flows between 2 objects because of their difference in temperature. Other forms of energy — • light • electrical • kinetic and potential Dr. S. M. Condren
Potential Energy in the Atomic Scale • Positive and negative particles (ions) attract one another. • Two atoms can bond • As the particles attract they have a lower potential energy NaCl — composed of Na+ and Cl- ions. http://mrsec.wisc.edu/Edetc/pmk/NaCl_alt.html Dr. S. M. Condren
Internal Energy (E) PE + KE = Internal energy (E or U) Int. E of a chemical system depends on • number of particles • type of particles • temperature 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 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 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 Dr. S. M. Condren
Exothermic Reaction First-Aid Hotpacks, containing either calcium chloride or magnesium sulfate, plus water Dr. S. M. Condren
Endothermic Reaction First-aid cold packs, containing ammonium nitrate and water in separate inner pouches Dr. S. M. Condren
Enthalpy • heat at constant pressure qp = DH = Hproducts - Hreactants Exothermic Reaction DH = (Hproducts - Hreactants) < 0 H2O(l) -----> H2O(s)DH < 0 Endothermic Reaction DH = (Hproducts - Hreactants) > 0 H2O(l) -----> H2O(g)DH > 0 Dr. S. M. Condren
Enthalpy H = E + PV DH = DE + PDV DE = DH – PDV Dr. S. M. Condren
First Law of Thermodynamics heat => q internal energy => E internal energy change =>DE work => w = - P*DV DE = q + w Dr. S. M. Condren
Specific Heat-Specific Heat Capacity • the amount of heat necessary to raise the temperature of 1 gram of the substance 1oC • independent of mass • substance dependent • s.h. • Specific Heat of Water = 4.184 J/goC Dr. S. M. Condren
Heat q = m * s.h. * Dt where q => heat, J m => mass, g s.h. => specific heat, J/g*oC Dt = change in temperature, oC, (always tf – ti) Dr. S. M. Condren
Molar Heat Capacity • the heat necessary to raise the temperature of one mole of substance by 1oC • substance dependent • C Dr. S. M. Condren
Heat Capacity • the heat necessary to raise the temperature 1oC • mass dependent • substance dependent • C Dr. S. M. Condren
Heat Capacity C = m X s.h. where C => heat capacity, J/oC m => mass, g s.h. => specific heat, J/goC Dr. S. M. Condren
Plotted are graphs of heat absorbed versus temperature for two systems. Which system has the larger heat capacity? A, B Dr. S. M. Condren
Heat Transfer qlost = - qgained (m X s.h. X Dt)lost = - (m X s.h. X Dt)gained Dr. S. M. Condren
Heat Transfer Dr. S. M. Condren
EXAMPLEIf 100. g of iron at 100.0oC is placed in 200. g of water at 20.0oC in an insulated container, what will the temperature, oC, of the iron and water when both are at the same temperature? The specific heat of iron is 0.106 cal/goC. (100.g*0.106cal/goC*(Tf - 100.)oC) = qlost - qgained = (200.g*1.00cal/goC*(Tf - 20.0)oC) 10.6(Tf - 100.oC) = - 200.(Tf - 20.0oC) 10.6Tf - 1060oC = - 200.Tf + 4000oC (10.6 + 200.)Tf = (1060 + 4000)oC Tf = (5060/211.)oC = 24.0oC Dr. S. M. Condren
Melting of Ice http://mrsec.wisc.edu/Edetc/pmk/ice.html Dr. S. M. Condren
EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0oC to steam at 127.0oC? q = DHice + DHfusion + DHwater + DHboil. + DHsteam q = DHice + DHfusion + DHwater + DHboil. + DHsteam Dr. S. M. Condren
Heat Transfer Dr. S. M. Condren
EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0oC to steam at 127.0oC?q = DHice + DHfusion + DHwater + DHboil. + DHsteam q = (10.0g*2.09J/goC*((0.0 – (-15.0))oC)) { specific heat of ice Mass of the ice Temperature change Dr. S. M. Condren
EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0oC to steam at 127.0oC?q = DHice + DHfusion + DHwater + DHboil. + DHsteam q = (10.0g*2.09J/goC*15.0oC) + (10.0g*333J/g) Melting of ice occurs at a constant temperature Mass of ice Heat of fusion Dr. S. M. Condren
EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0oC to steam at 127.0oC?q = DHice + DHfusion + DHwater + DHboil. + DHsteam q = (10.0g*2.09J/goC*15.0oC) + (10.0g*333J/g) + (10.0g*4.18J/goC*((100.0-0.00)oC)) Mass of water Specific heat of liquid water Temperature change of the liquid water Dr. S. M. Condren
EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0oC to steam at 127.0oC?q = DHice + DHfusion + DHwater + DHboil. + DHsteam q = (10.0g*2.09J/goC*15.0oC) + (10.0g*333J/g) + (10.0g*4.18J/goC*100.0oC) + (10.0g*2260J/g) Boiling of water occurs at a constant temperature Mass of water Heat of vaporization Dr. S. M. Condren
EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0oC to steam at 127.0oC?q = DHice + DHfusion + DHwater + DHboil. + DHsteam q = (10.0g*2.09J/goC*15.0oC) + (10.0g*333J/g) + (10.0g*4.18J/goC*100.0oC) + (10.0g*2260J/g) + (10.0g*2.03J/goC*((127.0-100.0)oC)) Specific heatof steam Temperature change for the steam Mass of steam Dr. S. M. Condren
EXAMPLE: How much heat is required to heat 10.0 g of ice at -15.0oC to steam at 127.0oC?q = DHice + DHfusion + DHwater + DHboil. + DHsteam q = (10.0g*2.09J/goC*15.0oC) + (10.0g*333J/g) + (10.0g*4.18J/goC*100.0oC) + (10.0g*2260J/g) + (10.0g*2.03J/goC*27.0oC) q = (314 )J + 3.33X103 + 4.18X103 + 2.26X104 + 548 = 30.96 kJ Dr. S. M. Condren
Spreadsheet of Previous Problem Dr. S. M. Condren
Coffee Cup Calorimeter Dr. S. M. Condren
Bomb Calorimeter 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 0.629oC. How much heat is gained by the calorimeter? heat gained = - heat lost heatcalorimeter + heatwater = heatreaction heatcalorimeter = heatreaction - heatwater 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 0.629oC. How much heat is gained by the calorimeter? heatcalorimeter = heatreaction - heatwater heat = 11.0 kJ - ((3.000kg)(0.629oC)(4.184kJ/kgoC)) = 3.10 kJ Dr. S. M. Condren
Example What is the mass of water equivalent of the heat absorbed by the calorimeter? #g = (3.10 kJ/0.629oC)(1.00kg*oC/4.184kJ) = 6.47 x 102 g 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 24.284oC to 26.225oC. Determine the heat for the reaction. m = (3000. + 647)g H2O q = m X s.h. X Dt = (3647g)(4.184J/goC)(1.941oC) = 29.61 kJ Dr. S. M. Condren