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Blake Lecture 9-26-08

Blake Lecture 9-26-08 - Blake Chemistry Heat and Chemistry...

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Blake 9-26-08 Chemistry Heat and Chemistry Energy changes E = q + w 1. Heat Change 2. Work (another type of energy change) 3. What drives the world and economy The signs are very important. We need to know if a system is gaining or losing energy 1. E = Change in internal E system 2. E = positive system gains E, negative = loses E 3. Gains heat q = + 4. Releases Heat q = - 5. Work Done On System = + 6. Work Done By System = - Heat Change and Temperature Change q = mc (delta T) m = mass, c = specific heat required to raise temp. 1 degree, change in temp. Specific Heat is how much it takes to change 1 gram of material 1 degree Celsius If you add heat to an object, its temperature will increase If 15.0 grams of water at 23 degrees Celsius gains 250 J of heat, what is its new temperature c = 4.184 J/g degrees C +250 J = (15 grams)(4.18 J/g degrees Celsius)(T f -23 C) Change is 4 degrees Celsius New Temperature is 27 degrees Celsius Phase Changes Heat of vaporization of water: 2256 J/g Heat of fusion of water: 333 J/g Vaporization of H 2 O H 2

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Blake Lecture 9-26-08 - Blake Chemistry Heat and Chemistry...

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