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Thermochemistry

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  1. Thermochemistry Feeling hot, hot, hot Unit 15

  2. New Seats! The rules: • If you are in the front, you must not be in the front anymore • If you are in the back, you must move to the front • You may not have the same neighbors • You must move at least two tables away from where you are now • If I don’t like your choice; I will move you

  3. Housekeeping • HW tonight- Specific Heat worksheet (half-sheet) • Sub on Friday

  4. Energy Energyis the capacity to do work • Thermal energy is the energy associated with the random motion of atoms and molecules • Chemical energy is the energy stored within the bonds of chemical substances • Nuclear energy is the energy stored within the collection of neutrons and protons in the atom • Electrical energy is the energy associated with the flow of electrons • Potential energy is the energy available by virtue of an object’s position

  5. 900C 400C Energy Continued Heat is the transfer of thermal energy between two bodies that are at different temperatures. Temperature is a measure of the thermal energy. Temperature = Thermal Energy greater thermal energy

  6. SURROUNDINGS SYSTEM Thermochemistry is the study of heat change in chemical reactions. The system is the specific part of the universe that is of interest in the study. closed isolated open energy nothing Exchange: mass & energy 6.2

  7. Heat transfer • Example: You place an ice cube into a bowl of hot soup. Describe the direction of heat flow. • The hotter soup transfers heat to the colder ice. • It is possible to transfer HEAT, but never COLD. (There is no such thing as cold transfer!)

  8. Thermochemistry heat • Thermochemistry – concerned with the changes that occur during a reaction. • Heat ( ) - that transfers from one object to another because of a between them. SI unit is the ( ). Heat always flows from a object to a object. chemical q energy temp. difference joule J warmer cooler

  9. Energy capacity • Energy – the for doing or supplying . work heat

  10. Law of COE • Law of Conservation of Energy – Energy is neither nor ; it can be from one form to another. • chemical reactions involve a or of heat. created destroyed transferred ALL release absorption

  11. Reactions exo - exit • Exothermic process – to its surroundings • Endothermic process – to its surroundings releases heat absorbs heat endo - enter

  12. Reactions

  13. Thermochemical Equations • 4Fe (s) + 3O2 (g) 2Fe2O3 (s) + 1625 kJ • Does this reaction give off heat or absorb heat? • Exothermic or endothermic?

  14. Thermochemical Equations • What does kJ mean? • (measurement of ) • ΔH - change in heat content for a reaction at constant pressure. Kilojoule = 1000 J heat Enthalpy

  15. Thermochemical Equations • C (s) + 2S (s) + 89.3 kJ  CS2 (l) • Is heat released or absorbed in this chemical reaction? • Exothermic or endothermic?

  16. Heat Capacity and Specific Heat • What does it mean to “burn calories”? generates which is measured in calories. • calorie –the quantity of energy needed to raise the temperature of 1 g of pure water 1 °C

  17. Calorie vs. calorie Calorie- dietary calorie – the energy in food calorie- “little c”- the quantity of heat needed to raise the temperature of 1 g of pure water 1 degree C

  18. Conversions • 1 Calorie= 1 kilocalorie= 1000 calories • 1Joule (J)= 0.2390 calories (little c!!!!!) • 1 kcalth = 4184 Joules (J) • 1 calorie= 4.184 Joules (J) • 1000g= 1kg • 1kJ= 1000 J

  19. Conversions • Convert 444 calories to joules.

  20. Heat capacity • Heat capacity – the quantity of energy needed to raise the temperature of an object 1 °C • Heat capacity depends upon the mass of the object and the chemical composition.

  21. Specific Heat Capacity • C = q m(ΔT) Where q= heat (joules of calories) M= mass (grams) ΔT= change in temperature (Celsius)

  22. Friday April 25th, 2014 You need: Notes notebook, pen/pencil, specific heat worksheet (half sheet) QOTD • An insulated cup contains 75.0g of water at 24.00oC. A 26.00g sample of metal at 82.25oC is added. The final temperature of the water and metal is 28.34oC. What is the specific heat of the metal? (ans 0.971 J/goC )

  23. Housekeeping HW- Group heat capacity (if not finished in class) Quiz on heat capacity Tues April 29th, 2014 Your job today- work in your group (your group only) on the specific heat worksheet given to today. You may work at a lab station or at the desks.

  24. Period 4 Groups 1- Hannah, Rezhaun, Jerome, Jessica 2- Noah, Jennifer, Essence, Trevon 3- Megha, Abby, Riley 4- Katie, Jeshsie, Jack 5- Maggie S., Kairo, Ian 6-Drew, Marcel, Julie, Joe 7- Marissa, Francis, Sam 8- Alexis, Christian, Alex, Vincent 9-Grif, Mary, Mackenzie

  25. Period 5 Groups 1- Jack, Tiel, Sarah, Jackson 2- Molly, Taylor, Daniel 3- Dylan, Ethan, Megan 4- Trent, Hein, Mathias 5- Aaron, Shen, Christian, Jesse 6- Yeji, Ray, Nick 7- Andrew, Joosje, Alyssa 8- Jeremiah, Catie, Zane 9- Meara, Skyler

  26. Period 6 Groups 1- Elle, Brendan, Moe, Linda 2- Sophie, Josh, Allise 3- Ryan, Quinn, Jacob 4- ChaeYeon, Brooke, Cameron 5- Maisy, Julia, Michael 6- Elizabeth, Lauren, Haley 7- Julia S., Jo Jo, Ciara, Roger 8- Blayke, Jacob, Luke 9-Charlotte, Luis, Connor

  27. Period 7 1- Tomas, Tatianna, Simon 2- Jack, Nathan, Michael 3- Matt, Aiman, Cole 4- Marissa, Stephen, Tyler 5- Nick, Sarah, Cassie 6- Audrey, Montana, Arthur 7- Murtaza, Frank, Elisa 8- Jenna, Jessica, Brian 9-Brett, Udit, Athan 10- Ijoo, Sarah Oh, Sujung

  28. Monday April 28th, 2014 You need: notes notebook, pen/pencil and group heat capacity worksheet to be checked for credit QOTD 1. What is the specific heat capacity of silver metal if 55.00 g of the metal absorbs 47.3 calories of heat and the temperature rises 15.0°C? 2. If a sample of chloroform is initially at 25°C, what is its final temperature if 150.0 g of chloroform absorbs 1.0 kilojoules of heat, and the specific heat of chloroform is 0.96 J/g°C? 3. How much energy must be absorbed by 20.0 g of water to increase its temperature from 283.0 °C to 303.0 °C? (Cp of H2O = 4.184 J/g °C)

  29. Housekeeping HW tonight- Review Packet (5 problems or areas) Specific heat capacity quiz- TUES APRIL 29th, 2014

  30. Heat Capacity vs. Specific Heat Capacity Heat capacity- for an object- depends on its mass heat required to raise temperature of an entire sample (ex: a full bucket of water) Units--------- Joules/°C Specific heat capacity- (of a substance) Heat required to raise 1 gram of the substance by 1 degree Celsius Units------- Joules/gram°C

  31. What we’ve learned so far…. C= q/mΔT Another way to look at the same equation (algebra!) q= CmΔT We can also have, q= ΔH= CmΔT where ΔH is ENTHALPY *this is true only when there is a constant pressure for the system

  32. Measuring/Expressing Heat Changes • Thermochemical equations – treat heat change ( ) just like any other or • Chemistry problems involving H are similar to problems – depends on number of of reactants and products involved. H reactant product stoichiometry moles

  33. Tuesday April 29th, 2014 You need: Notes notebook, pen/pencil, calculator, Group heat capacity worksheet QUIZ TODAY  Sit quietly and we will begin

  34. Conversions • 1 Calorie= 1 kilocalorie= 1000 calories • 1Joule (J)= 0.2390 calories (little c!!!!!) • 1 kcalth = 4184 Joules (J) • 1 calorie= 4.184 Joules (J) • 1000g= 1kg • 1kJ= 1000 J

  35. Housekeeping HW tonight- pre-lab for ALUMINUM CALORIMETRY * in thermochem section of gen chem website LAB on block day (PANTS!!!!!!!) LAST DAY for reactions re-take is TODAY!

  36. Wed/Thurs April 30th/May 1st 2014 You need: notes notebook, chapter 11 packet, group specific heat worksheet (graph one) and your pre-lab to be checked for credit QOTD • Gold has a specific heat of 0.129 J/(g×°C). How many joules of heat energy are required to raise the temperature of 15 grams of gold from 22 °C to 85°C?

  37. Housekeeping HW- finish chapter 11 packet if not finished in class today  Exam –Tuesday May 13th, 2014….. Talk about options…… Quiz- Hess’s Law next Tuesday May 6th, 2014

  38. Thermochemical equations • Have balanced atoms • Include energy term as: Reactant- if endothermic (energy will sit on reactants side) Product- if exothermic (energy will sit on products side)

  39. Heat of Reaction Symbolized as ΔHRXN (+) for endothermic (-) for exothermic ΔHRXN = Hproducts- Hreactants Products (low enthalpy (heat content)) Reactants (High enthalpy (heat content))

  40. Measuring/Expressing Heat Changes • CaO + H2O  Ca(OH)2 + 65.2 kJ and • 2CaO + 2 H2O 2 Ca(OH)2 + 130.4 kJ Multiply everything by 2

  41. Measuring/Expressing Heat Changes • 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.

  42. Friday May 2nd, 2014 You need: notes notebook, pen/pencil, heat capacity group work (graph), chapter 11 heat flow packet and lab data to be shared with the class.

  43. Housekeeping HW-NONE QUIZ- Tues May 6th, 2014- Hess’s Law Exam- Tues May 13th, 2014- thermochem Goal today- • Review group work • heat flow packet • share lab data and discuss lab • Continue Entropy notes

  44. Monday May 5th, 2014 You need: notes notebook, pen/pencil, heat flow packet (chapter 11) and your lab information (pre-lab with data)

  45. Housekeeping HW-NONE QUIZ- Wed/Thurs May 7th/8th, 2014- Hess’s Law Exam- Tues May 13th, 2014- thermochem Scoring guide will be passed out tomorrow

  46. Entropy S • Entropy ( ) – a measure of the of a system • For example, when playing cards are ordered by number and suit, they have a entropy ( ) • When a deck of cards is thrown into the air, they have a entropy ( ) disorder low organized high disorganized

  47. Entropy • Law of Disorder – Processes move in the direction of or . • (Things easily become disorganized – think about your bedroom!) increasing entropy disorder

  48. When does entropy (S) increase in a reaction? gas solid liquid • Phase change:  (increasing entropy) • When a substance is into parts NaCl Na+ + Cl- • When the total number of molecules total number of molecules • 2 SO3 + 1 CO2 1 CS2 + 4 O2 • When increases broken product reactant > temperature

  49. Entropy increasing • + S entropy/disorder • - S entropy/disorder decreasing

  50. Spontaneous Processes physical • A spontaneous process is a or change that occurs with outside . • Examples – iron methane ice chemical assistance no rusting burning melting