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AP CHEMISTRY CHAPTER 5

AP CHEMISTRY CHAPTER 5. Thermodynamics- the flow of heat. 5.1 Thermochemistry. A. kinetic NRG- NRG of motion KE = ½ mv 2 B. Potential NRG – stored NRG PE= mgh D. Chemical NRG- due to PE E. thermal NRG- due to temperature. 5.1 Con. F. units Joules= kg-m 2 /s 2

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AP CHEMISTRY CHAPTER 5

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  1. AP CHEMISTRY CHAPTER 5 Thermodynamics- the flow of heat

  2. 5.1 Thermochemistry • A. kinetic NRG- NRG of motion KE = ½ mv2 • B. Potential NRG – stored NRG PE= mgh • D. Chemical NRG- due to PE • E. thermal NRG- due to temperature

  3. 5.1 Con. • F. units Joules= kg-m2/s2 1 calorie = 4.184 J (exactly. EXACTLY, I say!) 1000 cal = 1Cal = 1kcal = 1 food calorie • G. system- what we are studying • H. surroundings- everything else • I. Universe = system + surroundings

  4. 5.1, Still • J.force- push or pull • K.work = force x distance • L.heat- NRG transfer from hotter to colder • M.energy- is the capacity to do work OR to transfer heat

  5. 5.2 First Law of ThermodynamicsIt is observed in this house! NRG is conserved OR NRG cannot be created or destroyed • A. internal NRG, E= KE + PE 1.) +Δ E = NRG gained by system 2.) - Δ E = NRG lost to surroundings • B. E = q + w 1.) E = internal NRG 2.) q= heat 3.) w = work

  6. 5.2 Con. • C.endothermic - absorbs heat ( ΔH= +) • D.exothermic – gives off heat (ΔH= -) • E.state function - does not depend on path, only initial and final values.

  7. 5.3 + 5.4 • 5.3 enthalpy- heat content of a system. A state function • 5.4 enthalpy of reaction (heat of reaction), an extensive property ΔH = products - reactants TABLE on p.189 Appendix C p. 1112

  8. Sample 5.3 p. 157 (Mass - heat Prob.) CH4 + 2O2 CO2 + 2H2O(l) + heat -74.8 0 -393.5 -285.8 kJ/mol ΔH= [(-393.5) + 2(-285.8)] – [-74.8 + 0] = -890.3 kJ/mol (exo) 4.50g CH4 x 1mol CH4 x –890.3 kJ 16.0 g CH4 1mol CH4 = -250 kJ

  9. 5.5 Calorimetry • A. calorimeter- apparatus that measures heat flow. • B. heat capacity- temp. change when substance absorbs heat. (extensive) • C. Molar heat capacity- heat capacity of 1 mol • D. specific heat- heat needed to raise 1 g of a substance to 1degreeC. (Cp) (intensive) between 15.5 and 16.5 degrees C Water = 1 cal = 4.18J/g-deg.C = 4.18J/g-K

  10. Calorimeter

  11. 5.6 • Hess’s Law – if a reaction is carried out in a series of steps, H for the reaction will be equal to the sum of enthalpy change for the individual steps. ( a state function)

  12. 5.7 Enthalpy of Formation (Heat of Formation) Sample p. 187 ∆Hf f= formed from 1mol of it’s elements • A. standard state 1 atm & 25 degrees C (298K) • B. standard enthalpy of formation, Hf, for any element is zero. H time

  13. Energy Profile Diagram ΔH = positive #

  14. ΔH = negative #

  15. q = m Cp ΔT • q = heat in Joules (J) • m = mass in grams • Cp = specific heat in J/g-oC • ΔT = change in temp in oC

  16. Slope = Δy/Δx

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