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Chapter 6 - Thermochemistry

Chapter 6 - Thermochemistry. Section 6.1 The Nature of Energy. Energy Law of Conservation of Energy Potential energy Kinetic energy Heat Work Pathway State function or property Chemical Energy. Chemical Energy. System Surroundings Exothermic Endothermic Thermodynamics

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Chapter 6 - Thermochemistry

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  1. Chapter 6 - Thermochemistry

  2. Section 6.1 The Nature of Energy • Energy • Law of Conservation of Energy • Potential energy • Kinetic energy • Heat • Work • Pathway • State function or property • Chemical Energy

  3. Chemical Energy • System • Surroundings • Exothermic • Endothermic • Thermodynamics • First Law of Thermodynamics • Internal energy • Problems – pages 246 - 248

  4. Section 6.2 Enthalpy and Calorimetry • Enthalpy ΔH = Hproducts – Hreactants • Sample problems – page 249 – 250 • Calorimetry q = c x m ΔT • Specific heat capacity • Molar heat capacity • Constant-pressure calorimetry • Problems page 251 – 256

  5. Section 6.3 Hess’s Law • Hess’s Law • Characteristics of Enthalpy changes • If a reaction is reversed, the sign of ΔH is also reversed. • The magnitude of ΔH is directly proportional to the quantities of reactants and products in a reaction. • Problems pages 258 - 259

  6. Section 6.4 Standard Enthalpies of Formation • Standard enthalpy of formation • Standard state

  7. Definitions of Standard States For a compound • The standard state of a gaseous substance is a pressure of exactly 1atm • For a pure substance in a condensed state (solid or liquid), the standard state is the pure liquid or solid • For a substance present in a solution, the standard state is a concentration of exactly 1M. For an element • The standard state of an element is the form in which the element exists under conditions of 1 atm and 25°C. (The standard state for oxygen is O2(g) at a pressure of 1 atm; the standard state for sodium is Na(s); the standard state for mercury is Hg(l).

  8. Calculating Enthalpy Changes ΔH°reaction =∑npΔH°f(products) - ∑npΔH°f(reactants) Problems pages 263 – 267 Reminders: * When a reaction is reversed, the magnitude of ΔH remains the same, but its sign changes. * When the balanced equation for a reaction is multiplied by an integer, the value of ΔH must be multiplied by the same integer. * Elements in their standard states are not included in ΔH°reaction calculations.

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