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Energy and Chemical Change

Energy and Chemical Change. Energy. How is energy in our everyday lives?. Cooks the food we eat Propels vehicles that transport us Allows photosynthesis to occur to start the food chain Energy from burning fuels heats or cools the classroom Allows you to think and write

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Energy and Chemical Change

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  1. Energy and Chemical Change Energy

  2. How is energy in our everyday lives? • Cooks the food we eat • Propels vehicles that transport us • Allows photosynthesis to occur to start the food chain • Energy from burning fuels heats or cools the classroom • Allows you to think and write • Cells are factories that run on energy derived from the food we eat

  3. What is energy? • The ability to do work or produce heat • Potential energy vs. kinetic energy – 2 basic forms • Potential energy – energy of position • Kinetic energy – energy of motion • Ex. Roller coaster

  4. Chemical systems • Contain both kinetic and potential energy • Kinetic energy – directly related to constant random motion of particles – prop. To temp. • Potential energy depends on composition – chemical bonds, arrangement of atoms, etc.

  5. Conservation of Energy • Energy can be neither created nor destroyed, it can only be converted from one form to another. • 1st Law of thermo.

  6. Heat • q • Energy flowing from a warmer object to a cooler object. • As energy flows, change in temperature • Calorie – energy needed to raise one gram of water one ºC. • When your body breaks down sugars and fats to form carbon dioxide and water, these reactions generate heat energy that can be measured in calories. • SI unit is the joule which equals 0.2390 calories.

  7. Specific heat (c) • 1J= 0.2390 calories, then one calorie equals… • 4.184 Joules. • 1 nutritional calorie = kcal • Pg. 492 practice problems • The specific heat of any substance is the amount of heat required to raise the temperature of one gram of that substance by one degree Celsius. • So, for water, that’s 4.184J/g·ºC

  8. Specific heat • Cp = q . m x ∆T Cp = specific heat q = heat absorbed or released by substance m= mass ∆T = change in temperature

  9. Specific heat • The relationship between heat and specific heat… • q=c·m·ΔT • qtotal=qwater + qmaterial • or • cwater ·mwater ·ΔTwater = cmaterial·mmaterial·ΔTmaterial • Table pg. 492

  10. Practice problems • Pg. 495 #’s 4-6

  11. Calorimeter • (Sounds like…?) • Is an insulated device to measure the change in heat during a chemical reaction.

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