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# Reaction Energy

Reaction Energy. Specific Heat. The specific heat of any substance is the amount of heat required to raise the temperature of one gram of that substance by one degree Celsius. Because different substances have different compositions, each substance has its own specific heat.

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## Reaction Energy

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1. Reaction Energy

2. Specific Heat • Thespecific heatof any substance is the amount of heat required to raise the temperature of one gram of that substance by one degree Celsius. • Because different substances have different compositions, each substance has its own specific heat.

3. Exothermic and Endothermic Exothermic: Heat flows out of the system (to the surroundings). The value of ‘q’ is negative. Endothermic: Heat flows into the system (from the surroundings). The value of ‘q’ is positive.

4. Specific Heat q = m CpΔT q = heat (J) Cp = specific heat (J/(g.°C) m = mass (g) ΔT = change in temperature = Tf – Ti(°C)

5. Measuring Heat • Heat changes that occur during chemical and physical processes can be measured accurately and precisely using a calorimeter. • Acalorimeteris an insulated device used for measuring the amount of heat absorbed or released during a chemical or physical process.

6. A coffee-cup calorimeter made of two Styrofoam cups.

7. Melting Vaporization Freezing Condensation Phase Changes Solid Gas Liquid

8. Sublimation Vaporization Deposition Melting Solid Gas Liquid Freezing Condensation

9. Latent Heat q = m Hv q = m Hf Hv = latent heat of vaporization (J/g) Hf = latent heat of fusion (J/g)

10. Energy and Phase Change • Heat of vaporization (Hv) is the energy required to change one gram of a substance from liquid to gas. • Heat of fusion (Hf) is the energy required to change one gram of a substance from solid to liquid.

11. Specific Heat Problem 1) The temperature of a sample of iron with a mass of 10.0 g changed from 50.4°C to 25.0°C with the release of 114 J heat.What is the specific heat of iron? (25.0 – 50.4) -114 = q = 10.0 m Ciron ∆T Ciron = 0.449 J/g°C

12. Specific Heat Problem 2) A piece of metal absorbs 256 J of heat when its temperature increases by 182°C. If the specific heat of the metal is 0.301 J/g°C, determine the mass of the metal. m = 4.67 g

13. Specific Heat Problem 3) If 335 g water at 65.5°C loses 9750 J of heat, what is the final temperature of the water? Tf = 58.5 °C

14. Specific Heat Problem 4) As 335 g of aluminum at 65.5°C gains heat, its final temperature is 300.°C.Determine the energy gained by the aluminum. q = 70500 J

15. Latent Heat Problem 5) How much heat does it take to melt 12.0 g of ice at 0 °C? q = 12.0 m Hf (334) q = 4010 J

16. Latent Heat Problem 6) How much heat must be removed to condense 5.00 g of steam at 100 °C? q = 5.00 m (2260) Hv q = 11300 J

17. Latent Heat Problem Lf = 67 J/g 7) If 335 J of heat are added to melting 5.00 g of gold, what is the latent heat of fusion for gold in J/g?

18. Latent Heat Problem m = 6.18 g 8) The latent heat of fusion for platinum is 119 J/g. Platinum absorbs 735 J of heat. What is the mass of platinum?

19. HEATING AND COOLING CURVES

20. The heating curve has 5 distinct regions.

21. The horizontal lines are where phase changes occur. vaporization melting

22. Kinetic energy increases on any diagonal line, and potential energy increases on any horizontal line. melting

23. The melting point temperature is equal to the freezing point temperature. The boiling point is the same as the temperature where condensation takes place. melting

24. Use q = m CpΔT for all diagonal lines. Use q = m Hf for melting and q = m Hv for boiling. melting

25. For a cooling curve, kinetic energy decreases on any diagonal line, and potential energy decreases on any horizontal line. melting

26. Heating/Cooling Curve Problem melting 9. What is the freezing point of the substance? FP = 5°C

27. Heating/Cooling Curve Problem melting 10. What is the melting point of the substance? MP = 5°C

28. Heating/Cooling Curve Problem melting 11. What is the boiling point of the substance? BP = 15°C

29. Heating/Cooling Curve Problem melting 12. What letter represents the temperature where the solid is being heated? A

30. Heating/Cooling Curve Problem melting 13. What letter represents the temperature where the vapor is being heated? E

31. Heating/Cooling Curve Problem melting • 14. What letter represents the temperature where the liquid is being heated? C

32. Heating/Cooling Curve Problem melting 15. What letter represents the melting of the solid? B

33. Heating/Cooling Curve Problem melting 16. What letters show a change in kinetic energy? A, C and E

34. Heating/Cooling Curve Problem melting • 17. What letter represents condensation? D

35. 18. What is the melting point of this substance? 19. At what time do the particles of this sample have the lowest average kinetic energy? Heating/Cooling Curve Problem melting 18. What is the freezing point of this substance? FP = 90°C

36. 18. What is the melting point of this substance? 19. At what time do the particles of this sample have the lowest average kinetic energy? Heating/Cooling Curve Problem melting 19. At what time do the particles of this sample have the lowest average kinetic energy? 16 min

37. 18. What is the melting point of this substance? 19. At what time do the particles of this sample have the lowest average kinetic energy? Heating/Cooling Curve Problem melting  20. How many minutes does it take the substance to condense? 4 min

38. Heating/Cooling Curve Problem melting 21. What is the temperature range for the substance to be a vapor? 150 <T < 205

39. Heating Curve for Water Section D: Water is Boiling. Section A: Ice is being heated to the melting point. Section C: Water is being heated to the boiling point. Section B: The ice is melting. Section E: Steam is being heated.

40. Section D q = mHv Heating Curve for Water Section E q = m CpΔT(gas) Section B q = mHf Section C q = m CpΔT(liquid) Section A q = m CpΔT(solid)

41. Solving Problems • For water: Melt Ice Heat Water Boil Water Heat Steam Heat Ice + + + + At 0°C 0°C - 100°C At 100°C Above 100°C Below 0°C

42. Specific Heat and Latent Heat 22) How much heat does it take to heat 12 g of ice at – 6 °C to 25 °C water? Round to a whole number. You begin at ice below 0 °C. Note: The final temperature for this process cannot exceed 0 °C. q = m 12 (2.05) Cice ∆T (0 - –6) q = 148 J

43. Specific Heat and Latent Heat, cont. • How much heat does it take to heat 12 g of ice at – 6 °C to 25 °C water? Round to a whole number. Since the temperature needs to rise to 25 °C, you must melt the ice next. q = 12 m (334) Hf q = 4008 J

44. Specific Heat and Latent Heat, cont. • How much heat does it take to heat 12 g of ice at – 6 °C to 25 °C water? Round to a whole number. You now have water at 0 °C. The final temperature of the water should be 25 °C. q = 12 m Cwater (4.18) (25 - 0) ∆T q = 1254 J

45. Specific Heat and Latent Heat, cont. • How much heat does it take to heat 12 g of ice at – 6 °C to 25 °C water? Round to a whole number. Finally, add all of the q values together. q = 148 + 4008 + 1254 q = 5410 J

46. Specific Heat and Latent Heat 23) How much heat does it take to heat 35 g of ice at 0°C to steam at 150°C? Round to a whole number. You begin with ice at 0 °C, so you should melt it first. q = 35 m (334) Hf q = 11690 J

47. Specific Heat and Latent Heat, cont. • How much heat does it take to heat 35 g of ice at 0°C to steam at 150°C? Round to a whole number. You now have water at 0 °C. The final temperature of the steam is to be 150 °C. You must take the water to 100 °Cbefore you can even convert it to steam. q = 35 m Cwater (4.18) (100 - 0) ∆T q = 14630 J

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