1 / 33

$$$ Review $$$ Thermochemistry

$$$ Review $$$ Thermochemistry. Gives off heat (emits). exothermic. $1. Absorbs heat. endothermic. $1. It flows from hot to cold objects and is known by the letter “q”. heat. $1. The study of energy changes that occur during chemical reactions. thermochemistry. $1.

rae-garza
Télécharger la présentation

$$$ Review $$$ Thermochemistry

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. $$$ Review $$$ Thermochemistry

  2. Gives off heat (emits) exothermic $1

  3. Absorbs heat endothermic $1

  4. It flows from hot to cold objects and is known by the letter “q” heat $1

  5. The study of energy changes that occur during chemical reactions thermochemistry $1

  6. What is a calorie or joule? Unit of heat (q) $1

  7. Defined as the amount of heat needed to increase the temperature of an object by 1oC. Heat capacity $2

  8. Defined as the amount of heat needed to increase 1 gram of an object by 1oC. Specific heat or specific heat capacity $1

  9. The formula for q? q = C x m x DT $2

  10. Solve the previous equation for the other three variables. C = q/mDT m = q/CDT DT = q/Cm $3

  11. A balance bar has 200 Calories. How many kilojoules is this? How many joules is this? 836.8 kj 836,800 joules $3

  12. True or False. cal/oC is an acceptable unit for specific heat. False, cal/goC $1

  13. True or False. Metals generally have a higher specific heat capacity than water. False $1

  14. True or False. Metals generally have a higher specific heat capacity than molecular compounds. False $1

  15. You measure 1200 joules of heat during a 30oC temperature change with a substance that weighs 100 g. What is the specific heat of the substance. 0.40 J/goC $3

  16. During a phase change, the temperature of a substance ________. Remains constant $1

  17. A calorimeter can effectively measure the heat of another substance because of the ____________? Law of Conservation of Energy $2

  18. DH of fusion involves which phase change? Melting $1

  19. DH of solidification involves which more commonly known phase change? Freezing $1

  20. If the percent mass of a solution weighing 300 g is 6%, what is the mass of the solute? .06 = x/300g x = 18 g $2

  21. The heat content of a system at a constant pressure is known as the ________ of that system. enthalpy $2

  22. What is the enthalpy change in a chemical reaction known as? Heat of reaction, DH $2

  23. If the DH of a reaction is negative then the reaction is _______ . exothermic $1

  24. The heat of the reaction for the complete burning of one mole of a substance. Heat of combustion $1

  25. The enthalpy change when a mole of solute is dissolved in a solvent. Heat of solution $1

  26. True or False. The quantity of heat absorbed when a solid melts is the same as the quantity released when the substance freezes. True. DHfus = -DHsolid. $1

  27. What makes Hess’s law useful? It allows you to determine heats of reactions indirectly $2

  28. The change in enthalpy that involves the formation of one mole of a compound from its elements (at 25oC) is known as? Standard heat of formation, (DHfo) $2

  29. True or False. The standard heat of a reaction can be calculated by the following equation … DHo = DHfo(products) - DHfo(reactants) True $1

  30. How to solve a phase change problem You just multiply DH of fusion/vaporization by mass Water is vaporizing DHvap= 2260 J/g of H2O q = m xDHvap Water is melting DHfus = 334 J/g of H2O q = m xDHfus (J)

  31. Heating/Cooling Curve: No Phase Changes What happens at A, C, and E?? We use our old formula q = m x C xDT q = m x Cgas x DT q = m x Cliq x DT q = m x Csolid x DT (J)

  32. Heating/Cooling Curve: Putting it all Together You should be able to calculate the total heat going all the way from heating a substance from its solid to its gas q = m x DHvap q = m x Cgas x DT q = m x Cliq x DT q = m x DHfus q = m x Csolid x DT (J)

  33. Sample Problem You have a 4.30 grams of ice at -13.2oC. You heat it until it completely vaporizes. How much heat was needed to complete this process? Here are some numbers you might need. (Cice = 2.10 J/goC) (Cwater = 4.18 J/goC) (Csteam = 1.70 J/goC) (DHfus = 334 J/g) (DHvap = 2260 J/g) To get answer you simply add these 4 numbers together: 13071 J or 13.1 kJ (3 sig. figs) q = m x Cice x DT (4.30)(2.10)(0.00 - -13.2)= 119.2 J q = m x DHfus (4.30)(334)= 1436.2 J q = m x Cwat x DT (4.30)(4.18)(100. - 0.00)= 1797.4 J q = m x DHvap = (4.30)(2260)= 9718 J

More Related