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Reaction Energy and Reaction Kinetics

Reaction Energy and Reaction Kinetics. Thermochemistry. Thermochemistry. Objectives: Define heat and temperature. Perform specific heat calculations. Temperature and Heat. Temperature – measure of the average kinetic energy of the particles of a substance. What are the units? o C, K

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Reaction Energy and Reaction Kinetics

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  1. Reaction Energy and Reaction Kinetics Thermochemistry

  2. Thermochemistry Objectives: • Define heat and temperature. • Perform specific heat calculations.

  3. Temperature and Heat Temperature – measure of the average kinetic energy of the particles of a substance. What are the units? oC, K Heat – the flow of energy from one substance to another. What are the units? Joules, calories, Calories, kJ, kcal 1 cal = 4.184 J

  4. Specific Heat (C): the amount of energy needed to raise the temperature of 1 gram of a substance by 1 degree celcius For water: C = 4.184 J/goC C = 1 cal/g0C Specific Heat

  5. Specific Heat q = heat (joule or cal) m= mass (grams) C = specific heat (J/g*C) or (cal/g*C) ΔT= change in temperature (oC)

  6. Specific Heat Problems • Determine the specific heat of a material if a 35 g sample absorbed 48 J as it was heated from 293K to 313K. • If 980 kJ of energy are added to 6.2 L of water at 18oC, what will the final temperature be?

  7. Heat of Reaction Enthalpy (H) – heat content of a system Enthalpy change (ΔH) – amount of energy absorbed or lost by a system during a process at constant pressure. ΔH = Hproducts- Hreactants

  8. Heat of Reaction

  9. Heat of Reaction Combustion of propane C3H8 (g) + 5 O2(g) 3 CO2 (g) + 4 H2O(g) + 2043 kJ ΔH = -2043 kJ (exothermic) Formation of synthesis gas C(s) + H2O(g) +113kJ  CO(g) + H2(g) ΔH = +113 kJ (endothermic)

  10. Sample Problems • How much heat will be released when 6.44 g of sulfur reacts with excess O2 according to the following equation? 2 S + 3 O2 2 SO3ΔH = -791.4 kJ • How much heat is transferred when 9.22 g of glucose (C6H12O6) in your body reacts with O2 according to the following equation? C6H12O6 (s) + 6 O2(g) 6 CO2 (g) + 6 H2O(l)ΔH= -2803 kJ

  11. Heat of Formation Molar Heat of Formation (∆Hf0) – energy change that occurs when 1 mole of a compound forms from the combination of its elements. H2(g) + 1/2O2(g) H2O(l) ∆Hf0= -285.8 kJ/mol C(s) + O2(g)  CO2(g) ∆Hf0 = -393.5 kJ/mol

  12. Stability and Heat of Formation Al2O3(s) -1676.0 kJ/mol CaCO3(s) -1206.92 kJ/mol NO(g) 90.29 kJ/mol O3(g) 142.7 kJ/mol • Stability goes with a high negative heat of formation.

  13. Heat of Combustion Heat of Combustion (∆Hc0) –energy released with the combustion of one mole of a substance. C3H8(g) + 5 O2(g) 3 CO2(g)+ 4 H2O(l) ∆Hc0= -2219.2 kJ/mol

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