Dunnoe Essay

2528 Words Jun 17th, 2014 11 Pages
Chapter 6 — Thermo — Part 1
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Chapter Scopes
• Endothermic & Exothermic reactions • Enthalpy changes: H of formation, combustion, hydration, neutralization, atomization. • Lattice energy, electron affinity • Heat of fusion and vaporization • Hess’ Law • Born-Haber cycles • Calorimetry

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CHAPTER 5

Chemical Energetic / Thermochemistry

© 2006 Brooks/Cole - Thomson

© 2006 Brooks/Cole - Thomson

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Energy & Chemistry
• ENERGY is the capacity to do work or transfer heat. • HEAT is the transfer of thermal energy between two objects because of their difference in temperature. Other forms of energy light electrical kinetic and potential
© 2006 Brooks/Cole - Thomson

Thermochemistry
• Thermochemistry is the study of
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• The heat (q) “lost” or “gained” is related to a) sample mass b) change in T and c) specific heat capacity
Specific heat capacity = heat lost or gained by substance (J) (mass, g)(T change, K)
© 2006 Brooks/Cole - Thomson

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Change in Temperature (T)
∆T of System Increase Sign of ∆Tsystem + Tfinal >Tinitial Tfinal < Tinitial Sign of q + Direction of Heat Transfer Heat transferred from surroundings to system (_____thermic) Heat transferred from system to surroundings (_____thermic)

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Decrease

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© 2006 Brooks/Cole - Thomson

Chapter 6 — Thermo — Part 1

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13 14 Example 1: If 25.0 g of Al cool from 310oC to 37oC, how many joules of heat energy are lost by the Al?

Heat Transfer q = m x Cs x ∆T q = C x ∆T
• • • • • q = heat absorbed or released (J) Cs = specific heat (J g-1 K-1) C = heat capacity (J K-1) m = mass of substance (g) ∆T = change in temperature (K) = Tfinal - Tinitial

(specific heat capacity of Al = 0.897 J g-1 K-1)
Solution: Heat gain/lose = q = (sp. ht.)(mass)( T) where T = Tfinal - Tinitial q= q=
Negative sign on q signals heat “lost by” or “transferred OUT” from

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