Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations


Presentation on theme: "Dr. S. M. Condren Chapter 6 Principles of Reactivity: Energy and Chemical Reactions."— Presentation transcript:

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

2 Dr. S. M. Condren Thermite Reaction

3 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

4 Dr. S. M. Condren Kinetic Energy

5 Dr. S. M. Condren Chemical Potential Energy

6 Dr. S. M. Condren Chemical Potential Energy

7 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.

8 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 = J = 1-kg*m 2 /sec 2

9 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

10 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

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

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

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

14 Dr. S. M. Condren 2 H 2(g) + O 2(g) --> 2 H 2 O (g) + heat and light 2 H 2 O (g) + heat and light This can be set up to provide ELECTRIC ENERGY in a. This can be set up to provide ELECTRIC ENERGY in a fuel cell.Oxidation: 2 H 2 ---> 4 H e - 2 H 2 ---> 4 H e -Reduction: 4 e - + O H 2 O ---> 4 OH - 4 e - + O H 2 O ---> 4 OH - Energy & Chemistry H 2 /O 2 Fuel Cell Energy, page 288

15 Dr. S. M. Condren is the capacity to do work or transfer heat. ENERGY is the capacity to do work or transfer heat. is the form of energy that flows between 2 objects because of their difference in temperature. HEAT is the form of energy that flows between 2 objects because of their difference in temperature. Other forms of energy Other forms of energy lightlight electricalelectrical kinetic and potentialkinetic and potential Energy & Chemistry

16 Dr. S. M. Condren 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. Potential Energy in the Atomic Scale

17 Dr. S. M. Condren PE + KE = Internal energy (E or U) Int. E of a chemical system depends on –number of particles –type of particles –temperature Internal Energy (E)

18 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

19 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

20 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

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

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

23 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

24 Dr. S. M. Condren Enthalpy H = E + PV E = H – P V

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

26 Dr. S. M. Condren Specific Heat-Specific Heat Capacity 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 = J/g o C

27 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, (always t f – t i )

28 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

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

30 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

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

32 Dr. S. M. Condren Heat Transfer q lost = - q gained (m X s.h. X t) lost = - (m X s.h. X t) gained

33 Dr. S. M. Condren Heat Transfer

34 Dr. S. M. Condren EXAMPLE If 100. g of iron at 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 cal/g o C. (100.g*0.106cal/g o C*(T f ) o C) = q lost - q gained = (200.g*1.00cal/g o C*(T f ) o C) 10.6(T f o C) = (T f o C) 10.6T f o C = T f o C ( )T f = ( ) o C T f = (5060/211.) o C = 24.0 o C

35 Dr. S. M. Condren Melting of Ice

36 Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at o C to steam at o C? q = H ice + H fusion + H water + boil. + steam q = H ice + H fusion + H water + boil. + steam

37 Dr. S. M. Condren Heat Transfer

38 Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at o C to steam at 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 {

39 Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at o C to steam at 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

40 Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at o C to steam at 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*(( ) o C)) Mass of water Specific heat of liquid water Temperature change of the liquid water

41 Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at o C to steam at 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

42 Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at o C to steam at 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*(( ) o C)) Mass of steam Specific heat of steam Temperature change for the steam

43 Dr. S. M. Condren EXAMPLE: How much heat is required to heat 10.0 g of ice at o C to steam at 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 X X X = kJ

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

45 Dr. S. M. Condren Coffee Cup Calorimeter

46 Dr. S. M. Condren Bomb Calorimeter

47 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 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

48 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 g of water was raised o C. How much heat is gained by the calorimeter? heat calorimeter = heat reaction - heat water heat = 11.0 kJ - ((3.000kg)(0.629 o C)(4.184kJ/kg o C)) = 3.10 kJ

49 Dr. S. M. Condren Example What is the mass of water equivalent of the heat absorbed by the calorimeter? #g = (3.10 kJ/0.629 o C)(1.00kg* o C/4.184kJ) = 6.47 x 10 2 g

50 Dr. S. M. Condren Example A g sample of ethanol was burned in the sealed bomb calorimeter described above. The temperature of the water rose from o C to o C. Determine the heat for the reaction. m = ( )g H 2 O q = m X s.h. X t = (3647g)(4.184J/g o C)(1.941 o C) = kJ

51 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

52 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

53 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

54 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 + · · ·

55 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

56 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 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

57 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

58 Dr. S. M. Condren Calculation of H o H o = c* H f o products - c* H f o reactants

59 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 L Text C 6 H 6(l) H f o = kJ/mol O 2(g) H f o = 0 CO 2(g) H f o = H 2 O (g) H f o = H rx c* H f o products - c* H f o reactants

60 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 L Text C 6 H 6(l) H f o = kJ/mol; O 2(g) H f o = 0 CO 2(g) H f o = ; H 2 O (g) H f o = H rx c* H f o products - c* H f o reactants H rx 1 mol) kJ/mol) + (6mol)( kJ/mol) products - 2mol)( kJ/mol) + (15mol)(0kJ/mol) reactants = x 10 3 kJ

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

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


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

Similar presentations


Ads by Google