Lecture4 - Review Chapter 6: Reaction Energetics and...

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1 Chapter 6 of Text Thermochemistry: Introduction to Thermodyamics Energy Flow and Chemical Change Review Chapter 6: Reaction Energetics and Enthalpy Definition of State Functions Definition of enthalpy to keep track of energy under constant pressure conditions (most common in lab) Hess’s Law of Heats Summation Important to World’s Energy Balance “Bank Account” and issues surrounding global warming First Law of Thermodynamics: Energy is conserved during a chemical reaction…….key enabling concept Review Problems Chapter 6: 8,15, 17, 22, 26,48, 49, 50, 54, 63, 65,70, 75,95,103, 108 - Be sure you can do these problems….do extra problems to build confidence - Reaction energetics is really a key concept in everything Thermochemistry: Energy Flow and Chemical Change 6.1 Forms of Energy and Their Interconversion heat and work 6.2 Enthalpy: Heats of Reaction and Chemical Change heat at constant pressure 6.3 Calorimetry: Laboratory Measurement of Heats of Reaction concept of temperature/heat…measure temp. change gives heat or enthalpy of reaction 6.4 Stoichiometry of Thermochemical Equations 6.5 Hess’s Law of Heat Summation State Functions and First Law of Thermodynamics…energy is conserved 6.6 Standard Heats of Reaction ( Δ H 0 rxn ) Hess’ Law using standard states of matter to enable predictions for nearly all chemical reactions
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2 Thermodynamic s An elegant means to mathematically connect a few basic Laws of Nature to powerfully predict outcomes First Law of Thermodynamics: Energy is conserved during a chemical reaction (all else falls from this concept) When energy is transferred from one object to another, it appears as work and/or as heat. For our work we must define a system to study; everything else then becomes the surroundings . The system is composed of particles with their own internal energies (E or U). Therefore the system has an internal energy. When a change occurs, the internal energy changes. Figure 6.1 A chemical system and its surroundings. the system the surroundings Δ E = E final -E initial = E products reactants Figure 6.2 Energy diagrams for the transfer of internal energy (E) between a system and its surroundings. Definition of a State Function Path Independent “Fall from building hurts the same whether one takes the stairs or elevators” Figure 6.3 A system transferring energy as heat only.
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3 Figure 6.4 A system losing energy as work only. Energy, E Zn(s) + 2H + (aq) + 2Cl - (aq) H 2 (g) + Zn 2+ (aq) + 2Cl - (aq) Δ E<0 work done on surroundings Table 6.1 The Sign Conventions* for q , w and Δ E qw += Δ E + + - - - - + + + - depends on sizes of q and w depends on sizes of q and w * For q : + means system gains heat; - means system loses heat.
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Lecture4 - Review Chapter 6: Reaction Energetics and...

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