1 / 38

Chapter 5

Chapter 5. Thermochemistry. Terms I. Thermochemistry Study of Kinetic Energy Energy of Potential Energy Energy of. Units of E. JOULE Calorie vs. calorie 1 Cal = 1 cal is the amount of heat necessary to raise the temperature of 1 g of water 1 o C 1 cal = J.

yagil
Download Presentation

Chapter 5

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 5 Thermochemistry

  2. Terms I • Thermochemistry • Study of • Kinetic Energy • Energy of • Potential Energy • Energy of

  3. Units of E • JOULE • Calorie vs. calorie • 1 Cal = • 1 cal is the amount of heat necessary to raise the temperature of 1 g of water 1oC • 1 cal = J

  4. Terms II • Force • A • Work • Energy used to move an object • W = • Energy • Capacity to do

  5. First Law of Thermodynamics • Energy • Δ E =

  6. Equation II • Δ E = • q = heat in or heat out of system • w = work done on or by the system

  7. Practice • Calculate the change in the internal energy of the system for a process in which the system absorbs 140 J of heat from the surroundings and does 85 J of work on the surroundings.

  8. Endothermic Reaction • Process when a system • Gets • ΔH >

  9. Exothermic Reaction • Process when a system • Gets • ΔH <

  10. State Function • Describes the condition of a system • Does not matter how the system got there • For example…

  11. ENTHALPY • Heat… • Represented by • Is a

  12. Enthalpy Equation • ΔH = Hfinal – Hinitial = qp • P indicates constant pressure

  13. Enthalpy of Reaction • ΔHrxn = H(products) – H(reactants) • 2H2O (g) 2H2 (g) + O2 (g)ΔH = • 2H2 (g) + O2(g) 2H2O(g) ΔH = Return

  14. Rules for Enthalpy and RXNS • Enthalpy is an extensive property • Enthalpy for a reaction • Enthalpy change depends on state of reactants and products

  15. Practice • 2Mg(s) + O2(g) 2MgO(s)ΔH=-1204 kJ • Is this • How much heat is transferred when 2.40 g of Mg are reacted? • How many grams of MgO are produced during an enthalpy change of 96.0 kJ?

  16. Continued • 2Mg(s) + O2(g) 2MgO(s)ΔH=-1204 kJ • How many kJ of heat are absorbed when 7.50 g of MgO(s) are decomposed into magnesium and oxygen at constant pressure?

  17. Calorimetry • The study of • Heat capacity (C): • Temperature change of an object as it • Amount of heat required to • Greater heat capacity means…

  18. Calorimetry • Molar heat capacity (Cmolar) • Specific heat capacity (Cp) • Equation:

  19. Calorimetry • What is the heat required to raise 400.00 g of water by 34.50oC? • What is the heat lost when 200.00 g of iron changes from 115.50 oC to 22.00 oC?

  20. Calorimetry • Large beds of rocks are used in some solar heated homes to store heat. Assume that the specific heat of rock is 0.082 J/g-K. Calculate the quantity of heat absorbed by 50.0 kg of rocks if their temperature increases by 12.0 oC

  21. Flashback… • Law of conservation of energy (First law of thermodynamics):

  22. Calorimetry • You have heated a 55.00 g piece of iron, Cp = 0.385 J/g-K, to 200.00 oC. You then put the iron into water in a calorimeter. There are 300.00 g of water at 22.00 oC. What is the final temperature of the mixture?

  23. Calorimetry • In the calorimetry lab you will be mixing an acid and a base and studying the temperature changes. • You mix 35.00 mL each of 1 M HCl and 1 M NaOH in a calorimeter. The temperature increases from 21.0 to 27.5 oC. What is the enthalpy change for the reaction in kJ/mol HCl?

  24. Hess’s Law

  25. Enthalpy of Formation • Energy change for the formation • Symbolized by Hf • Tables are for standard conditions • 1 atm • 25oC • Appendix C

  26. Enthalpy of Formation • Units for Hof are in • Magnitude depends on state • 2H2(g) + O2(g) 2 H2O(l)Hof = -285.8 • 2H2(g) + O2(g) 2 H2O(g)Hof = -241.8

  27. Enthalpy of Formation • By definition: the standard enthalpy of formation of the most stable form of ANY element is 0 kJ/mol • Hof C(s) = 0 • Hof H2(g) = 0

  28. Enthalpy of RXN • Horxn = Σn Hof (products) - Σm Hof (reactants)

More Related