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Unit 3: Thermochemistry

Unit 3: Thermochemistry. the study of heat changes associated with physical and chemical reactions. “first word”. Example of a “first word”. Mrs. Thompson’s Monday . As you listen to the story, jot down any key words you think have something to do with Thermochemistry.

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Unit 3: Thermochemistry

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  1. Unit 3: Thermochemistry the study of heat changes associated with physical and chemical reactions

  2. “first word”

  3. Example of a “first word”

  4. Mrs. Thompson’s Monday • As you listen to the story, jot down any key words you think have something to do with Thermochemistry. • What were some of the words you wrote down?

  5. Key words • Energy: the ability to do work or produce heat. • Heat: energy in the process of flowing from warmer objects to cooler ones. • Temperature: a measurement. (We will look at temperature in a couple of slides)

  6. Let’s take a closer look at energy… • 2 Types of energy: KINETIC ENERGY AND POTENTIAL ENERGY • Energy: the ability to do work or produce heat. • 1) KINETIC ENERGY: energy of movement (molecular movement). It has everything to do with temperature. example: flowing water out of dam gates There are 3 kinds of KINETIC ENERGY a) Vibrational – molecular bonds vibrate b) Rotational – molecule rotates c) Translational – molecule moves through space from point to point

  7. 2) POTENTIAL ENERGY: stored energy due to position or composition (types of atoms, # of bonds, types of bonds, the particular way atoms are arranged). example: water stored behind a dam (position) Let’s look at some examples of kinetic and potential energy. Ask yourself, “Does this have the potential to do something? Or is it doing something?”

  8. What about someone on a swing? Is this an example of potential energy or kinetic energy? Be careful!

  9. Measuring Heat • Temperature: measures average kinetic energy of molecules (how fast they move). Units in 0C or K • Heat: thermal energy “in transit” or “flowing”. Units in J (joules) • If you were to heat up water, the temperature change is a response to faster moving particles. • Heat is lost to the surroundings. example: Mrs. Thompson’s coffee cup losing heat the her hands

  10. Measuring Heat • The amount of heat required to raise the temperature of 1g of pure water by 10C or 1K is defined as a CALORIE (cal). • This is not to be confused with the nutritional Calorie which is actually 1kcal=1000 calories. • The SI unit of heat = Joules (J), 1 calorie = 4.18J • What does the word ENTHALPY mean? The total heat content of a chemical system.

  11. 1. Specific Heat Capacity • The amount of heat to raise the temperature of 1g of any substance by 10C/1K. • Each substance has its own specific heat because each has a different composition. Ex) H2O = 4.18 J g • 0C

  12. 2. Molar Heat Capacity • The amount of heat to raise the temperature of 1 mol of any substance by 10/1 K. Ex) H2O = 75.3 J K • mol

  13. 3. Total Heat • The amount of heat to raise the temperature of any amount of substance by any change in temperature. molar heat capacity Specific heat capacity H = nc H = mc mol Change in temperature Mass (g) Change in temperature • Is everyone still on the bus??

  14. Ex) Determine the heat required to raise the temperature of 100.0g of water from 250C to 100.00C. **note: T(final) – T(initial) H = m TC H = (100.0g)(100.00C-250C)(4.18J/g0C) H = 31350 J H = 31000J

  15. Calorimetry • A calorimeter is an insulated device used for measuring the heat change during a chemical or physical process.

  16. Ex) A mass of 100.0g of water is placed in a coffee cup calorimeter. The water temperature is measured to be 14.40C. A mass of 412g of calcium metal at a temp. of 40.60C is placed into the calorimeter. When the reaction is complete, the temp. of both the water and calcium is recorded as 24.60C. A) What is the heat absorbed by the water? B) What is the heat released by the calcium? C) What is the specific heat of calcium?

  17. A) H H2O= m TC H = (100.0g)(24.60C-14.40C)(4.18J/g0C) H = 4263.6 J H = 4260 J absorbed by H2O If 4260 J was absorbed by water, then 4260 J must have been released by calcium! So the answer is -4260 J. C) HCa = m TC C = H =(-4260 J) mT (412 g)(24.60C-40.60C) = 0.646 J/g0C

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