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Chapter 5.1-5.3

Chapter 5.1-5.3. Thermochemistry. Thermochemistry. Thermo means heat or energy Energy: Capacity of doing work Work: Force x displacement. Types of Energy. Kinetic Energy (KE) Energy due to motion E k = ½ mv 2 Where m = mass & v = velocity. Types of Energy.

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Chapter 5.1-5.3

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  1. Chapter 5.1-5.3 Thermochemistry

  2. Thermochemistry • Thermo means heat or energy • Energy: Capacity of doing work • Work: Force x displacement

  3. Types of Energy • Kinetic Energy (KE) • Energy due to motion • Ek = ½ mv2 • Where m = mass & v = velocity

  4. Types of Energy • Potential energy (PE) • Energy due to position Gravity higher PE lower PE • Units: Calorie (cal), Joule (J) • 1 Cal = 4.184 J

  5. System • Where we focus our attention • Surroundings • Everything else

  6. First Law of Thermodynamics • Energy is conserved Piston pushed up & work (W) done by the gas (say 6 J) 10 J added (q)

  7. First Law of Thermodynamics • What happens to the difference (10 – 6)? • Retained inside. (causes Internal energy change, ΔE): 10 = 4 + 6 q (Heat applied) = ? q = ΔE + W (first law Thermodynamics) or ΔE = q-W (here -W, Work done by the gas) • ΔE = q +W (here +W, Work done on the gas) • Note: Two different sign conventions exist

  8. Enthalpy (H) ΔE = q-W (work done by a gas) q = ΔE + W q = ΔE + P ΔV ΔH = ΔE + P ΔV (constant pressure) H = E + PV

  9. Enthalpy or heat Content (H) Begin End 2H2 + O2 2H2O Say 484 kJ 1 kJ • Note: 484 kJ is the Heat content of the reactants (HR) and 1 kJ is the heat content of the products (HP).

  10. Enthalpy or heat Content (H) ΔH = Hp –HR = 1 – 484 = -483 kJ (exothermic) • Here, initial heat content> Final heat cont. • What happens to the difference? • It is given off.

  11. Enthalpy or heat Content (H) 2H2O  2H2 + O2 1 kJ (HR) 484 kJ (HP) Is heat absorbed or given off? Heat is absorbed ΔH = Hp –HR = 484 – 1 = 483 kJ (endothermic) • Here, initial heat cont < Final heat cont

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