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ch07 In class presentation

# ch07 In class presentation - Chapter 7 Energy and Chemical...

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Chapter 7: Energy and Chemical Change Energy is the ability to do work and supply heat Work is motion against an opposing force 2 2 1 KE Energy Kinetic mv = =

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Potential energy (PE) is the energy of position or internal arrangement
KE can be converted into PE and vice versa When the child is at points (a) and (c) they have only PE; at point (b) only KE. Total energy is conserved (PE + KE = constant). When fully compressed or extended only PE; at natural length only KE. Total energy is conserved.

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The SI unit of energy is the joule ( J )
A 2 kg object moving at 1 meter per second has 1 J of kinetic energy You may also encounter the calorie ( cal ) ( 29 (exactly) J 4.184 cal 1 s m kg 1 kg) (2 J 1 -2 2 2 s 1 m 1 2 1 = = =

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The energy that is transferred as heat comes from the object’s internal energy The energy associated with the motion of the object’s molecules is referred to as its molecular kinetic energy The internal energy is often given the symbol E or U We are interested in the change in E : reactants products initial final or - E E E - E E E = =
The temperature of an object is related to the average kinetic energy of its atoms and molecules The temperature for curve (1) is lower than for curve (2) because the average kinetic energy is lower.

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Heat is a transfer of energy due to a temperature difference
The object we are interested in is called the system Everything outside the system is called the surroundings A boundary separates the system from the surroundings

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Open systems can gain or lose mass and energy across their boundaries Closed systems can absorb or release energy, but not mass, across their boundaries Isolated systems cannot exchange energy or matter with their surroundings
When heat is gained by an object, it is written as a positive number When heat is lost by an object, it is written as a negative number A spontaneous change is one that continues on its own Heat flows spontaneously from a warmer to colder object The heat directly gained or lost by an object is directly proportional to the temperature change it undergoes

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The object’s specific heat ( C ) relates the heat ( q ) to the objects temperature change The heat capacity is the amount of heat needed to raise the object’s temperature by one degree Celsius and has the units J/°C C is an extensive property that can be determined from experiment, and is proportional to the sample mass t C ) - t C (t q = = initial final
The

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ch07 In class presentation - Chapter 7 Energy and Chemical...

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