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Unit 13 Thermochemistry

Unit 13 Thermochemistry. Day 1: Intro to Thermochemistry Videos and Alka Seltzer Lab (p.2-4). Energy and Chemistry: Crash Course Chemistry # 17 Enthalpy: Crash Course Chemistry #18. Alka Seltzer Lab. Step 1- Determine and record the active ingredients of Alka Seltzer tablets.

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Unit 13 Thermochemistry

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  1. Unit 13 Thermochemistry

  2. Day 1: Intro to Thermochemistry Videosand Alka Seltzer Lab (p.2-4) Energy and Chemistry: Crash Course Chemistry #17 Enthalpy: Crash Course Chemistry #18

  3. Alka Seltzer Lab • Step 1- Determine and record the active ingredients of Alka Seltzer tablets. • Step 2 - Add about 1/4 cup (60 mL) of room-temperature water into a clear container. Add an Alka Seltzer tablet to the water and observe. Describe what happens. What role does water play in this system? What is the identity of the most obvious product of this chemical change? • Step 3 - Design an experiment to determine the impact of changes in the temperature of the water on the system.

  4. Day 2: Thermochemistry Review and Enthalpy Warm-up: How can you tell if a reaction is endothermic or exothermic? Notes: p. 5-7 HW: p. 8-9

  5. Thermochemistry • Thermochemistry focuses on the energychanges that occur during a chemicalreaction. • Heat(q) – Energythat transfers from one object to another because of a temperature difference between them. The standard international unit (SI unit) of heat is the joule (J). **Note: Heat always flows from a warmer object to a cooler object. • Enthalpy(H) – the heat content of a system at a constant pressure. • Energy – the capacityfor doing workor supplying heat.

  6. Law of Conservation of Energy • Law of Conservation of Energy – Energy is neither creatednor destroyed; but it can be transformedfrom one form to another. • Allchemical reactions involve a lossor gainof heat. • Exothermic process – Releases heat to its surroundings (Temperature of the system decreases) • Endothermic process – Absorbs heat from its surroundings (Temperature of the system increases)

  7. Energy Diagrams • The following graph shows the energy change during the reaction A + B → C. • Activationenergy: the amount of energy which a set of reactantshas to have in order for a chemical change to take place. • Does the product have more or less energy than the reactants? __________, • Would the reaction be endothermic or exothermic? _____________________. Heat is _______________. more gained Endothermic

  8. Why the hump?

  9. Thermochemical equations • A thermochemical equation is a balanced equation for a reaction that also includes heat. *Thermochemical equations must be balanced. • Heat of Reaction (ΔH) = the change of heat for a reaction under constant pressure. Also known as change in enthalpy.

  10. Heat of the reaction (ΔH)

  11. Examples 1: 4Fe (s) + 3O2 (g) 2Fe2O3 (s) + 1625 kJ • Does this reaction release heat or absorb heat? How much?_____ • What does kJ mean? _____________ (measurement of ________) • Endothermic or exothermic? 2: C (s) + 2S (s) + 89.3 kJ  CS2 (l) • Is heat released or absorbed in this reaction? How much?_______ • Endothermic or exothermic? 1625kJ energy kilojoules ΔH = -1625kJ 89.3kJ ΔH = 89.3kJ

  12. Thermochemical equations • Thermochemical equations treat heat change (ΔH) just like any reactantor product. • Chemistry problems involving H are similar to stoichiometryproblems; they depend on the number of molesof reactants and products involved, for example: CaO(s) + H2O(l) Ca(OH)2 (s) + 65.2 kJ and 2CaO(s) + 2 H2O(l)2 Ca(OH)2 (s) + 130.4 kJ *You must multiply the heat of reaction by the number of moles.

  13. 1H2 (g) + 1 F2 (g) 2HF(g)H = -536 kJ 2 2 4 then H = 2(-536 kJ) = -1072 kJ

  14. 2Al (s) + Fe2O3(s) Al2O3 (s) + 2Fe (s)H = -851 kJ 8 4 4 8 4 (-851 kJ) = -3404 kJ

  15. K2O (s) + H2O (l) 2KOH (aq)H = 215 kJ ½ ½ 1 ½ ( 215) = 107.5 kJ

  16. Homework Complete pages 9-10.

  17. Practice Problem #1 H2 (g) + F2 (g) 2HF(g)H = -536 kJ Calculate the heat change (in kJ) for the conversion of 10.1 g of H2 gas to HF gas at constant pressure. -536kJ 1 mole H2 10.1g H2 1 1 mole H2 2.016 g H2 = -2685.3kJ = -2690kJ

  18. Practice Problem #2 2Al (s) + Fe2O3(s) Al2O3 (s) + 2Fe (s)H = -851 kJ Calculate the heat change (in kJ) for the thermite reaction of 320 g of Fe2O3 into Al2O3 at constant pressure 320g Fe2O3 1 1 mole H2 159.687 g Fe2O3 -851kJ 1 mole Fe2O3 = -1705kJ = -1700kJ

  19. Practice Problem #3 K2O (s) + H2O (l) 2KOH (aq)H = 215 kJ What is the heat change for the above reaction, at constant pressure if you begin with 282.6 g of K2O? 1 mole K2O 94.196 g K2O 282.6g K2O 1 215kJ 2 mole K2O = 322.514kJ = 323kJ

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