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Entry Task: Oct. 1 st Monday

Entry Task: Oct. 1 st Monday. Question: Define Hess’s Law (in your own words) You have 5 minutes!. Agenda:. Discuss Hess’s Law (review from 1 st year) In-class problems (see backside of notes) HW: Pre-Lab Hess’s Law Lab. I can….

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Entry Task: Oct. 1 st Monday

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  1. Entry Task: Oct. 1st Monday Question: Define Hess’s Law (in your own words) You have 5 minutes!

  2. Agenda: • Discuss Hess’s Law (review from 1st year) • In-class problems (see backside of notes) • HW: Pre-Lab Hess’s Law Lab

  3. I can… • Manipulate thermochemical equations (Hess Law) to find enthalpy.

  4. Hess’s Law • H is well known for many reactions, and it is inconvenient to measure H for every reaction in which we are interested. • However, we can estimate H using published H values and the properties of enthalpy.

  5. Hess’s Law Hess’s law states that “[i]f a reaction is carried out in a series of steps, H for the overall reaction will be equal to the sum of the enthalpy changes for the individual steps.”

  6. Hess’s Law Because H is a state function, the total enthalpy change depends only on the initial state of the reactants and the final state of the products.

  7. Sample Exercise 5.8Using Three Equations with Hess’s Law to Calculate H Calculate Hfor the reaction 2 C(s) + H2(g) C2H2(g) given the following chemical equations and their respective enthalpy changes: Flip Double keep 226.8 kJ

  8. Sample Exercise 5.8Using Three Equations with Hess’s Law to Calculate H Practice Exercise Calculate H for the reaction NO(g) + O(g) NO2(g) given the following information Answer: –304.1 kJ keep Flip Flip divide by 2

  9. 5.51 Desired: P4O6(g) + 2O2 (g)  P4O10(s) ΔH = ? • P4(s) + 3O2 (g)  P4O6(g) ΔH = -1640.1 • P4(s) + 5O2 (g)  P4O10(g) ΔH = -2940.1 Flip keep -1300 kJ

  10. 5.53 Desired: C2H4(g) + 6F2(g)  2CF4(g) + 4HF (g) ΔH = ? • H2(s) + F2(g)  2HF(g) ΔH = -537 • C(s) + 2F2(g)  CF4(g) ΔH = -680 • 2C(s) + 2H2(g)  C2H4(g) ΔH = +52.3 double double Flip -2486.3 or -2.49x10-3 kJ

  11. Applying Hess law With the following data: a. S(s) + O2(g)  SO2 (g) ΔH of -297 kJ b. 2SO3(g)  2SO2(g) + O2(g) ΔH of 198kJ Use Hess law to calculate ΔH for 2S(s) + 3O2(g)  2SO3(g) double Flip

  12. We want to find out: 2S(s) + 3O2(g)  2SO3(g) ΔH = ? • 2S(s) + 2O2(g)  2SO2 (g) ΔH of -594 kJ • 2SO2(g) + O2(g)  2SO3 (g) ΔH of -198kJ • 2S(s) + 3O2(g)  2SO3(g) ΔH = -792 kJ

  13. Applying Hess law With the following data: a. 2H2(g) + O2 (g)  2H2O(l) ΔH= -527 kJ b. H2(g) + O2(g)  H2O2(l) ΔH= -188 kJ Use Hess law to calculate ΔH for 2H2O2(l)  2H2O(l) + O2 (g) Keep Flip and double

  14. We want to find out: 2H2O2(l)  2H2O(l) + O2 (g) ΔH = ? • 2H2O2(l)  2H2O(l) + O2 (g) ΔH = -151.0 kJ 2H2O2(l)  2H2(g) + 2O2(g) 376kJ -527kJ 2H2(g) + 2H2O(l) O2 (g) 

  15. Desired: 2CO(g) + 2NO (g)  2CO2(g) + N2(g) ΔH= ? a. 2CO(g) + O2 (g)  2CO2(g) ΔH = -566.0 kJ b. N2(g) + O2(g)  2NO(g) ΔH= 180.6kJ 2CO(g) + O2 (g)  2CO2(g) ΔH = -566.0 kJ b. 2NO(g)  O2(g) + N2(g) ΔH= -180.6kJ 2CO(g) + 2NO (g)  2CO2(g) + N2(g) ΔH= -746.6kJ

  16. Desired: 4Al(s) + 3MnO2(s) 2Al2O3(s) + 3Mn(s) ΔH= ? a. 4Al(s) + 3O2 (g)  2Al2O3 (s) ΔH = -3352 kJ b. Mn(s) + O2(g)  MnO2(s) ΔH= -521 kJ • 4Al(s) + 3O2 (g)  2Al2O3 (s) ΔH = -3352 kJ b. 3MnO2(s)  3Mn(s) + 3O2(g) ΔH= 1563 kJ 4Al(s) + 3MnO2(s)  2Al2O3(s) + 3Mn(s) ΔH= -1789kJ

  17. H2O (g) + C (s)  CO (g) + H2 (g) ΔH= ? • H2 (g) + ½ O2 (g)H2O (g) ΔH = - 242.0 kJ • 2CO (g)  2 C (s) + O2 (g) ΔH = + 221.0 kJ • H2O(s)  ½ O2 (g) + H2 (g) ΔH = 242.0kJ b. C(s) + ½ O2 (g)  CO(g) ΔH = -110.5kJ H2O (g) + C (s)  CO (g) + H2 (g) ΔH= 131.5kJ

  18. 2CO (g) + O2 (g)  2CO2 (g) =ΔH? C (s) + O2 (g)  CO2 (g) ΔH = - 393.5 kJ C (s) + ½ O2 (g) CO (g) ΔH = - 110.5 kJ 2C (s) + 2O2 (g)  2CO2 (g) ΔH = - 787kJ 2CO(g)  O2(g) + 2C (s) ΔH = 221kJ 2CO (g) + O2 (g)  2CO2 (g) ΔH= -566kJ

  19. C2H4 (g) + H2 (g)  C2H6 (g) =ΔH? C2H4 (g) + 3 O2 (g)  2 CO2 (g) + 2 H2O (l) ΔH -1411 kJ C2H6 (g) + 3½ O2 (g) 2 CO2 (g) + 3 H2O (l)ΔH = -1560 kJ H2 (g) + ½ O2 (g)  H2O (l) ΔH = -285 kJ H2 (g) + ½ O2 (g)  H2O (l) ΔH = -285. kJ C2H4 (g) + 3 O2 (g)  2 CO2 (g) + 2 H2O (l) ΔH -1411 kJ 2 CO2 (g) + 3 H2O (l) C2H6 (g) + 3½ O2 (g) ΔH= 1560 kJ C2H4 (g) + H2 (g)  C2H6 (g) ΔH= -136kJ

  20. YOUR TASK TONIGHT • Pre-Lab Hess’s Lab- IN JOURNAL!!!

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