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Heat Calculations

Heat Calculations. Agenda Review specific heat Look at lab sections M&M and Results Learn about heating curve. What is specific heat?. The energy to raise one gram of a substance one degree Celsius. What has a higher specific heat: the ocean or the beach?.

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Heat Calculations

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  1. Heat Calculations Agenda • Review specific heat • Look at lab sections • M&M and Results • Learn about heating curve

  2. What is specific heat? The energy to raise one gram of a substance one degree Celsius.

  3. What has a higher specific heat: the ocean or the beach? The OCEAN – it takes a lot of energy to warm it up!

  4. What has a higher specific heat: aluminum foil or the glass pan? The GLASS PAN – holds the heat for a much longer period of time

  5. Define energy. The ability to do work!

  6. When a reaction releases energy in the form of heat, it is said to be… EXOTHERMIC This means it’s negative!

  7. When a reaction absorbs energy in the form of heat, it is said to be… ENDOTHERMIC This means it’s positive.

  8. What is the formula for finding heat? q = m*s*DT

  9. What are the different units used to measure energy? Joule and Calorie Related? 1 cal = 4.184 J

  10. What happens if there is a phase change????? This is where the heating curve comes in…

  11. Heat Calculations Date:

  12. T E M P E R A T U R E E N E R G Y

  13. T E M P E R A T U R E GAS CONDENSE VAPORIZE 100OC LIQUID FREEZE MELT 0OC SOLID E N E R G Y

  14. T E M P E R A T U R E GAS CONDENSE VAPORIZE 100OC LIQUID FREEZE MELT 0OC SOLID ENDOTHERMIC g EXOTHERMIC f E N E R G Y

  15. T E M P E R A T U R E q = m*DHvap DHvap = 540cal/g GAS CONDENSE VAPORIZE 100OC q = m*DHfusion DHfusion = 80 cal/g q = m*s*DT Sgas = 0.4cal/goC LIQUID q = m*s*DT sliquid = 1cal/goC FREEZE MELT 0OC q = m*s*DT sice = 0.5cal/goC SOLID ENDOTHERMIC g EXOTHERMIC f E N E R G Y

  16. Solving Problems • Read question and determine number of “lines” involved. • Calculate the amount of heat required for each “line” • Determine the sum of all “lines” used. • IF ENERGY IS RELEASED, you MUST make DHfus and DHvap negative!!!!

  17. Calculate the amount of heat necessary to raise 20g H2O from -10oC to 45oC • Determine lines: -10oC = solid, 45oC = liquid so 3 lines used. • Solid: q = m*sice*DT q = (20g)(0.5cal/goC)(0oC – (-10oC)) = • Melt: q = m*DHfus q = (20g)(80cal/g) = • Liquid: q = m*sliquid*DT q = (20g)(1cal/goC)(45oC – 0oC) = TOTAL AMOUNT OF HEAT =

  18. Calculate the amount of heat released when 30g H2O are cooled from 115oC to 65oC • Determine lines: 65oC = liquid, 115oC = gas so 3 lines used. • Gas: q = m*sgas*DT q = (30g)(0.4cal/goC)(100oC – 115oC) = • Condensed: q = m*DHfus q = (30g)(-540cal/g) = • Liquid: q = m*sliquid*DT q = (30g)(1cal/goC)(65oC – 100oC) = TOTAL AMOUNT OF RELEASED HEAT =

  19. Suppose the heat needed to melt 38.0g of ice is absorbed from water contained in a glass. If this water has a mass of 210. g and an initial temperature of 21.0oC, what is the final temperature of the water? Remember the ice melts and then warms up as a liquid.

  20. Check homework

  21. Lab • M&M: • how was calorimeter constructed • when were temperature and mass readings made – not what but when • don’t list supplies • does it make sense – can you picture the lab like a movie • Results: Charts • Data used for calculations – Table 1 • Temperature over time GRAPH!!!!! Graph 1 • Show a sample calculation (q = msDT)

  22. Homework • Heat Calculations worksheet • Make corrections to MM and Results • Put data into spreadsheet from wiki • Work on conclusions

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