Presentation is loading. Please wait.

Presentation is loading. Please wait.

Principles of Reactivity: Energy and Chemical Reactions

Similar presentations


Presentation on theme: "Principles of Reactivity: Energy and Chemical Reactions"— Presentation transcript:

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

2 Thermite Reaction Dr. S. M. Condren

3 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

4 Kinetic Energy Dr. S. M. Condren

5 Chemical Potential Energy
Dr. S. M. Condren

6 Chemical Potential Energy
Dr. S. M. Condren

7 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

8 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

9 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

10 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

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

12 System and Surroundings
The object under study SURROUNDINGS Everything outside the system Dr. S. M. Condren

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

14 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

15 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

16 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

17 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

18 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

19 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

20 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

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

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

23 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

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

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

26 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

27 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

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

29 Heat Capacity the heat necessary to raise the temperature 1oC
mass dependent substance dependent C Dr. S. M. Condren

30 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

31 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

32 Heat Transfer qlost = - qgained
(m X s.h. X Dt)lost = - (m X s.h. X Dt)gained Dr. S. M. Condren

33 Heat Transfer Dr. S. M. Condren

34 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

35 Melting of Ice http://mrsec.wisc.edu/Edetc/pmk/ice.html
Dr. S. M. Condren

36 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

37 Heat Transfer Dr. S. M. Condren

38 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

39 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

40 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

41 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

42 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

43 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

44 Spreadsheet of Previous Problem
Dr. S. M. Condren

45 Coffee Cup Calorimeter
Dr. S. M. Condren

46 Bomb Calorimeter Dr. S. M. Condren

47 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

48 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

49 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

50 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

51 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

52 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

53 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

54 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

55 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

56 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

57 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

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

59 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

60 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

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

62 Based on 1998 Data Dr. S. M. Condren


Download ppt "Principles of Reactivity: Energy and Chemical Reactions"

Similar presentations


Ads by Google