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**Principles of Reactivity: Energy and Chemical Reactions**

Chapter 6 Principles of Reactivity: Energy and Chemical Reactions Dr. S. M. Condren

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Thermite Reaction Dr. S. M. Condren

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**Terminology Energy Kinetic Energy Potential Energy capacity to do work**

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

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Kinetic Energy Dr. S. M. Condren

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**Chemical Potential Energy**

Dr. S. M. Condren

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**Chemical Potential Energy**

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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

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**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 = J = 1-kg*m2/sec2 Dr. S. M. Condren

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**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

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**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

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**Thermochemistry Terminology**

system => that part of the universe under investigation surroundings => the rest of the universe universe = system + surroundings Dr. S. M. Condren

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**System and Surroundings**

The object under study SURROUNDINGS Everything outside the system Dr. S. M. Condren

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**Learn@UW will be unavailable**

Announcement will be unavailable on Thursday July 19 from 5:00am until 12:00 noon. Dr. S. M. Condren

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**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 e- Reduction: 4 e- + O H2O ---> 4 OH- H2/O2 Fuel Cell Energy, page 288 Dr. S. M. Condren

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**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

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**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. Dr. S. M. Condren

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**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

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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

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**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

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**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

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Exothermic Reaction First-Aid Hotpacks, containing either calcium chloride or magnesium sulfate, plus water Dr. S. M. Condren

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Endothermic Reaction First-aid cold packs, containing ammonium nitrate and water in separate inner pouches Dr. S. M. Condren

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**Enthalpy Exothermic Reaction Endothermic Reaction**

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

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Enthalpy H = E + PV DH = DE + PDV DE = DH – PDV Dr. S. M. Condren

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**First Law of Thermodynamics**

heat => q internal energy => E internal energy change =>DE work => w = - P*DV DE = q + w Dr. S. M. Condren

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**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 = J/goC Dr. S. M. Condren

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**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

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Molar Heat Capacity the heat necessary to raise the temperature of one mole of substance by 1oC substance dependent C Dr. S. M. Condren

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**Heat Capacity the heat necessary to raise the temperature 1oC**

mass dependent substance dependent C Dr. S. M. Condren

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**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

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**Plotted are graphs of heat absorbed versus temperature for two systems**

Plotted are graphs of heat absorbed versus temperature for two systems. Which system has the larger heat capacity? A, B Dr. S. M. Condren

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**Heat Transfer qlost = - qgained**

(m X s.h. X Dt)lost = - (m X s.h. X Dt)gained Dr. S. M. Condren

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Heat Transfer Dr. S. M. Condren

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**EXAMPLE If 100. g of iron at 100. 0oC is placed in 200**

EXAMPLE If 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 cal/goC. (100.g*0.106cal/goC*(Tf )oC) = qlost - qgained = (200.g*1.00cal/goC*(Tf )oC) 10.6(Tf oC) = (Tf oC) 10.6Tf oC = Tf oC ( )Tf = ( )oC Tf = (5060/211.)oC = 24.0oC Dr. S. M. Condren

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**Melting of Ice http://mrsec.wisc.edu/Edetc/pmk/ice.html**

Dr. S. M. Condren

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**q = DHice + DHfusion + DHwater + DHboil. + DHsteam**

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

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Heat Transfer Dr. S. M. Condren

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**EXAMPLE: How much heat is required to heat 10. 0 g of ice at -15**

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

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**EXAMPLE: How much heat is required to heat 10. 0 g of ice at -15**

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

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**EXAMPLE: How much heat is required to heat 10. 0 g of ice at -15**

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*(( )oC)) Mass of water Specific heat of liquid water Temperature change of the liquid water Dr. S. M. Condren

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**Boiling of water occurs at a**

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

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**EXAMPLE: How much heat is required to heat 10. 0 g of ice at -15**

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*(( )oC)) Mass of steam Specific heat of steam Temperature change for the steam Dr. S. M. Condren

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**EXAMPLE: How much heat is required to heat 10. 0 g of ice at -15**

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 = ( )J + 3.33X103 + 4.18X103 + 2.26X104 + 548 = kJ Dr. S. M. Condren

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**Spreadsheet of Previous Problem**

Dr. S. M. Condren

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**Coffee Cup Calorimeter**

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Bomb Calorimeter Dr. S. M. Condren

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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

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EXAMPLE A 1.000g sample of a particular compound produced 11.0 kJ of heat. The temperature of the calorimeter and 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

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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

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Example A g sample of ethanol was burned in the sealed bomb calorimeter described above. The temperature of the water rose from oC to oC. Determine the heat for the reaction. m = ( )g H2O q = m X s.h. X Dt = (3647g)(4.184J/goC)(1.941oC) = kJ Dr. S. M. Condren

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**exothermic, endothermic**

When graphite is burned to yield CO2, 394 kJ of energy are released per mole of C atoms burned. When C60 is burned to yield CO2 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 Dr. S. M. Condren

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**Laws of Thermochemistry**

1. The magnitude of DH is directly proportional to the amount of reactant or product. s --> l DH => heat of fusion l --> g DH => heat of vaporization Dr. S. M. Condren

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**Laws of Thermochemistry**

2. DH for a reaction is equal in magnitude but opposite in sign to DH for the reverse reaction. H2O(l) > H2O(s) DH < 0 H2O(s) > H2O(l) DH > 0 Dr. S. M. Condren

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**Laws of Thermochemistry**

3. The value of H for the reaction is the same whether it occurs directly or in a series of steps. DHoverall = DH1 + DH2 + DH3 + · · · Dr. S. M. Condren

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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 Dr. S. M. Condren

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**EXAMPLE CH4(g) + 2 O2(g) -----> CO2(g) + 2 H2O(l)**

CH4(g) > C(s) H2(g) DH1 2 O2(g) > 2 O2(g) DH2 C(s) + O2(g) > CO2(g) DH3 2 H2(g) + O2(g) > 2 H2O(l) DH4 CH4(g) O2(g) > CO2(g) H2O(l) DHoverall = DH1 + DH2 + DH3 + DH4 Dr. S. M. Condren

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**Standard Enthalpy of Formation**

the enthalpy associated with the formation of a substance from its constituent elements under standard state conditions Dr. S. M. Condren

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**DHo = Sc*DHfoproducts - Sc*DHforeactants**

Calculation of DHo DHo = Sc*DHfoproducts - Sc*DHforeactants Dr. S. M. Condren

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**Example What is the value of DHrx for the reaction: 2 C6H6(l) + 15 O2(g) --> 12 CO2(g) + 6 H2O(g)**

from Appendix L Text C6H6(l) DHfo = kJ/mol O2(g) DHfo = 0 CO2(g) DHfo = H2O(g) DHfo = D Hrx = [S c* D Hfo]products - [S c* D Hfo]reactants Dr. S. M. Condren

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Example What is the value of DHrx for the reaction: 2 C6H6(l) O2(g) --> 12 CO2(g) H2O(g) from Appendix L Text C6H6(l) DHfo = kJ/mol; O2(g) DHfo = 0 CO2(g) DHfo = ; H2O(g) DHfo = D Hrx = [S c* D Hfo]products - [S c* D Hfo]reactants DHrx = [(12mol)( kJ/mol) + (6mol)( kJ/mol)]products - [(2mol)( kJ/mol) + (15mol)(0kJ/mol)]reactants = x 103 kJ Dr. S. M. Condren

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Fossil Fuels coal petroleum natural gas Dr. S. M. Condren

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Based on 1998 Data Dr. S. M. Condren

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