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Thermochemistry

Thermochemistry. Study of heat in chemical reactions. Heat will travel between a system and its surroundings Heat is measured in Joules (J) Metric  English: BTU (British Thermal Unit) 1 BTU = 1.06 kJ.

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Thermochemistry

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  1. Thermochemistry • Study of heat in chemical reactions. • Heat will travel between a system and its surroundings • Heat is measured in Joules (J) • Metric  English: BTU (British Thermal Unit) • 1 BTU = 1.06 kJ

  2. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter08/Text_Images/FG08_02.JPG][http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter08/Text_Images/FG08_02.JPG]

  3. Calculating Heat • The heat that transfers between substances can be calculated with the following equation: q = (s) (m) (∆T)

  4. Calculating Heat • q : amount of heat (energy) transferred • s: specific heat • m: mass (use density to change from mL to g!) • ∆T: change in temperature

  5. Calculating Heat • Specific Heat is the quantity of heat needed to raise one gram of a substance 1.0 ⁰C. • Each specific substance has its own specific heat. (pg. 394)

  6. Round to 4.18 [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter08/Text_Images/FG08_TB01.JPG]

  7. Calculating Heat • Example: • How much heat is needed to warm a 200.0 mL cup of coffee (H2O) from 20.0 ⁰C to 75.0 ⁰C?

  8. Calculating Heat • 45980 J, but only 3 significant digits so…. • 4.60 x 104 J or 46.0 kJ

  9. Calculating Heat What is the specific heat of lead? 28.8 °C 20.0 °C 100.0 °C

  10. 1st Step - Calculate “q” for the H2O 20.0 °C q = 1840 J

  11. 2nd Step - Calculate “s” for Lead Energy that water absorbed in step one was supplied by the metal! 100.0 °C q = (150.0 g)(s)(71.2oC) 1840 J s = 0.172 J/(g x C) for Lead

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