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Thermochemistry

Thermochemistry. Chapter 11 sections 2 and 3. Calorimetry. Measurement of the heat into or out of a system. The heat released = the heat absorbed Calorimeter: device used to measure the heat Enthalpy (H): heat content of a system at constant pressure. Calorimetry.

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Thermochemistry

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  1. Thermochemistry Chapter 11 sections 2 and 3

  2. Calorimetry • Measurement of the heat into or out of a system. • The heat released = the heat absorbed Calorimeter: device used to measure the heat Enthalpy (H): heat content of a system at constant pressure

  3. Calorimetry • Changes in enthalpy = ∆H • Q = ∆H (these will both be used) • Q = ∆H = mC∆T • ∆H is negative for exothermic • ∆H is positive for endothermic

  4. Heat in Changes of State 1. Molar Heat of Fusion (∆Hfus)=heat absorbed by one mole of the substance during melting a solid to a liquid q= mol x ∆Hfus 2. Molar Heat of Solidification (∆Hsolid)= heat lost when one mole of a liquid solidifies (freezes) to a solid q= mol x ∆Hsolid * Heat absorbed by melting = heat lost when solidifies

  5. Energy required to melt 1 gram of a substance at its melting point Enthalpy of Fusion (DHfus) Heating Curve: ( For Water) Temp DHfus Melting point (°C) 0 -10 Heating Ice (solid) -20 Time

  6. After the substance melts and if heating continues, the temperature will continue to rise until it reaches its boiling point. ۞The temperature remains the same until all the substance has boiled.*** Energy and Change of State

  7. Enthalpy of Vaporization (DHvap) Boiling Point 100 DHfus DHvap Temp Heating Water (liquid) Melting Point 0 (°C) -10 Heating Ice -20 Time Energy required to vaporize 1 gram of a substance at its boiling point

  8. ► Important Formulas to Know ◄ When a substance is being heated, use the following formula: (inclined line-on graph) q = (m)(c)(DT) When a substance is melting or boiling, use the following formula: (flat line-on graph) q = (m) (DHfus or DHvap)

  9. q = (m)(c)(DT) (C) = Specific Heat: - of ice = 2.06 J/g x °C - of water = 4.18 J/g x °C - of steam = 2.02 J/g x °C

  10. q = (m) (DHfus or DHvap) Enthalpy Values for Water: DHfus = 334 J/g DHvap = 2260 J/g

  11. Sample Problem #1 How much heat is required to melt 5.67g of ice? Q = (m)(ΔH fus) Q = (5.67g)(334 J/g) Q =

  12. Sample Problems 2. How much energy is required to boil 85g of water? 3. How much energy is required to convert 40g of ice at -10°C to steam at 150°C ? 4. What is the final temperature when 1250 J of energy is added to 15g of water at 25°C ?

  13. Sample Problem #5 How much energy is required to raise the temperature of 25g of water from 15°C to 75°C ?

  14. Practice Problems How much energy is required to boil 50 grams of water? What is the final temperature when 2500 J of heat is added to 35 grams of water at 15 degrees Celsius? How much energy is required to convert 75 grams of ice at -20 degrees Celsius to steam at 125 degrees Celsius? (Hint: This problem has 5 steps!!)

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