Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Energy The capacity to do work or to produce heat.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Law of Conservation of Energy Energy can be converted from one form to another but can neither be created nor destroyed. (E universe is constant)
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 The Two Types of Energy Potential: due to position or composition - can be converted to work Kinetic: due to motion of the object KE = 1 / 2 mv 2 (m = mass, v = velocity)
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Temperature v. Heat Temperature reflects random motions of particles, therefore related to kinetic energy of the system. Heat involves a transfer of energy between 2 objects due to a temperature difference
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 State Function Depends only on the present state of the system - not how it arrived there. It is independent of pathway.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 System and Surroundings System: That on which we focus attention Surroundings: Everything else in the universe Universe = System + Surroundings
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Exo and Endothermic Heat exchange accompanies chemical reactions. Exothermic: Heat flows out of the system (to the surroundings). Endothermic: Heat flows into the system (from the surroundings).
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Figure 6.2 The Combustion of Methane
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Figure 6.3: The Energy Diagram for the Reaction of Nitrogen and Oxygen to Form Nitric Oxide
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 First Law First Law of Thermodynamics: The energy of the universe is constant.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 First Law E = q + w E = change in system’s internal energy q = heat w = work
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Work work = force distance since pressure = force / area, work = pressure volume w system = P V
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Figure 6.4 The Volume of a Cylinder
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Enthalpy Enthalpy = H = E + PV E = H P V H = E + P V At constant pressure, q P = E + P V, where q P = H at constant pressure H = energy flow as heat (at constant pressure)
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Heat Capacity
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Some Heat Exchange Terms specific heat capacity heat capacity per gram = J/°C g or J/K g molar heat capacity heat capacity per mole = J/°C mol or J/K mol
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Hess’s Law Reactants Products The change in enthalpy is the same whether the reaction takes place in one step or a series of steps.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Calculations via Hess’s Law 1. If a reaction is reversed, H is also reversed. N 2 (g) + O 2 (g) 2NO(g) H = 180 kJ 2NO(g) N 2 (g) + O 2 (g) H = 180 kJ 2. If the coefficients of a reaction are multiplied by an integer, H is multiplied by that same integer. 6NO(g) 3N 2 (g) + 3O 2 (g) H = 540 kJ
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Standard Enthalpies of Formation See the C (gr) → C (d) example. The standard enthalpy of formation ( H ˚ f ) of a compound is the change in enthalpy that accompanies the formation of one mole of the compound from its elements with all substances in their standard states.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Standard States Compound 4 For a gas, pressure is exactly 1 atmosphere. 4 For a solution, concentration is exactly 1 molar. 4 Pure substance (liquid or solid), it is the pure liquid or solid. Element 4 The form [N 2 (g), K(s)] in which it exists at 1 atm and 25°C.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Change in Enthalpy Can be calculated from enthalpies of formation of reactants and products. H rxn ° = n p H f (products) n r H f (reactants)
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Equation (6.1) H ˚ rxn = Σn p H ˚ f (products) - Σn r H ˚ f (reactants) Elements are not included in this calculation because elements require no change in form. You can find H ˚ f values on p. A-21, appendix. See the methods box on p See S/E 6.9, p 264: let’s do this using 6.1
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Figure 6.11 Energy Sources Used in the United States
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 An Opinion It has been proposed that the vast coal deposits formed from plants once living in the carboniferous period have resulted from the absence of any life on earth, especially the fungi or certain saprophytic bacteria, that possessed the ability to digest cellulose. So, they just piled up and were eventually buried… today’s coal.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Figure 6.12 The Earth’s Atmosphere
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Figure 6.13 Atmospheric CO 2 Concentration
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Figure 6.14 Coal Gasification