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Unit 3:

Unit 3: . Heat Transfer and Enthalpy of Change. Kinetic Energy  “motion” Moving electrons within an atom The vibration of atoms connected by chemical bonds The rotation/translation of molecules . Potential Energy  “position” Stored energy

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Unit 3:

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  1. Unit 3: Heat Transfer and Enthalpy of Change

  2. Kinetic Energy “motion” Moving electrons within an atom The vibration of atoms connected by chemical bonds The rotation/translation of molecules Potential Energy “position” Stored energy CHEMICAL ENERGY (other term)  arises from the forces (chemical bonds) that bind atoms together in a compound. Recall that the INTERNAL Energy of a system: + NO Is it possible to calculate the exact value of the internal energy?

  3. Molar Enthalpies (review) Molar Enthalpy: Hx = nHx absorbed released -  Hx +  Hx

  4. Enthalpy Changes in Chemical Reactions • In chemical reactions, enthalpy changes result from chemical bonds being broken or formed • Chemical bonds are sources of stored energy • Pg. 307 (table 1 and 2)

  5. Heat of Reaction (reminder!) The amount of heat released or absorbed during a chemical reaction. Endothermic: Reactions in which energy is absorbed as the reaction proceeds. Exothermic: Reactions in which energy is released as the reaction proceeds.

  6. NaOH dissolves in water • Qualitative observations • Quantitative observations • KNO3 dissolves in water • Qualitative observations • Quantitative observations DETERMINE the ENTHALPY of A REACTION (guided discovery) Materials: probe, coffee-cup calorimeter, file(OUT/science/SCH4U0-petro/lab title)

  7. NaOH dissolves in water • Qualitative observations • Quantitative observations Change in Ep of all atoms

  8. KNO3 dissolves in water • Qualitative observations • Quantitative observations Change in Ep of all atoms

  9. Endothermic Reactions Hfinall Hinitial Hf > Hi ∆H is positive

  10. Exothermic Reactions Hinitial Hfinall Hf < Hi ∆H is negative

  11. T(system) goes down T(surr) goes up T(system) goes up T (surr) goes down ENDOTHERMIC EXOTHERMIC

  12. H2O (s) H2O (l) DH = 6.01 kJ Thermochemical Equations Is DH negative or positive? System absorbs heat Endothermic DH > 0 6.01 kJ are absorbed for every 1 mole of ice that melts at 00C and 1 atm. 6.3

  13. DH = -890.4 kJ CH4(g) + 2O2(g) CO2(g) + 2H2O (l) Thermochemical Equations Is DH negative or positive? System gives off heat Exothermic DH < 0 890.4 kJ are released for every 1 mole of methane that is combusted at 250C and 1 atm. 6.3

  14. SO4-2 Cl q Examples What is the sign of H for: SO3-2(aq) + OCl(aq) SO4-2(aq) + Cl(aq) H 0 <

  15. NH4+ NO3 q Examples What is the sign of H for: NH4NO3(s) NH4+(aq) + NO3(aq) H 0 >

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