Ch-6-Thermochemistry - Chapter 6 Thermochemistry...

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Chapter 6
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2 Thermochemistry Thermochemistry is the study of the quantity of heat absorbed or evolved by chemical reactions. Thermodynamics is the science of the relationship between heat and other forms of energy.
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3 Nature of Energy Energy is anything that has the capacity to do work Work is a force acting over a distance Energy = Work = Force x Distance Energy can be exchanged between objects through contact collisions
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4 Classification of Energy Kinetic energy is energy of motion or energy that is being transferred thermal energy is kinetic
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5 Kinetic Energy Kinetic Energy: An object of mass m and speed or velocity ν has kinetic energy E k equal to 2 2 1 k mv E = m = mass (kg) v = velocity (m/s)
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6 Example Consider the kinetic energy of a person whose mass is 130 lb (59.0 kg) traveling in a car at 60 mph (26.8 m/s).
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7 Classification of Energy Potential energy is energy that is stored in an object, or energy associated with the composition and position of the object energy stored in the structure of a compound is potential
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8 Potential Energy Potential Energy: This energy depends on the “position” (such as height) in a “field of force” (such as gravity). o For example, water of a given mass m at the top of a dam is at a relatively high “position” h in the “gravitational field” g of the earth. mgh E p =
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9 Example Consider the potential energy of 1000 lb of water (453.6 kg) at the top of a 300 foot dam (91.44 m).
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10 Law of Conservation of Energy Energy cannot be created or destroyed First Law of Thermodynamics Energy can be transferred between objects Energy can be transformed from one form to another heat light sound
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11 Some Forms of Energy Electrical kinetic energy associated with the flow of electrical charge Heat or Thermal Energy kinetic energy associated with molecular motion Light or Radiant Energy kinetic energy associated with energy transitions in an atom Nuclear potential energy in the nucleus of atoms Chemical potential energy in the attachment of atoms or because of their position
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The SI unit of energy is the joule, J, The calorie is a non-SI unit of energy commonly used by chemists. It was originally defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius: 2 2 s m kg J = (exact) J 4.184 cal 1 = Energy Units James Joule 1818-1889
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13 Units of Energy joule (J) is the amount of energy needed to move a 1 kg mass a distance of 1 meter 1 J = 1 N m = 1 kgm 2 /s 2 calorie (cal) is the amount of energy needed to raise one gram of water by 1°C kcal = energy needed to raise 1000 g of water 1°C food Calories = kcals Energy Conversion Factors 1 calorie (cal) = 4.184 joules (J) (exact) 1 Calorie (Cal) = 1000 calories (cal) 1 kilowatt-hour (kWh) = 3.60 x 10 6 joules (J)
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14 System and Surroundings System The object under study Surroundings Everything outside the system
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Ch-6-Thermochemistry - Chapter 6 Thermochemistry...

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