CHM1311 - Lecture(7)

CHM1311 - Lecture(7) - Thermochemistry Thermochemistry The...

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Thermochemistry Thermochemistry The energy changes involved in chemical reactions The energy changes involved in chemical reactions 1 Petrucci Chapter 7 Petrucci Chapter 7
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Energy Energy The capacity to do work or to produce heat. Burning peanuts supply Burning peanuts supply sufficient energy to boil a cup sufficient energy to boil a cup of water. of water. Burning sugar (sugar reacts with KClO 3 ) CHEMICAL ENERGY CHEMICAL ENERGY 2
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Potential and Kinetic Energy Potential and Kinetic Energy KE = Potential Energy Potential Energy : Energy available to a system due to the position or composition of the system Energy can be classified as either kinetic or potential Kinetic Kinetic : Energy available due to the motion of an object e.g. a ball rolling down a hill e.g. a stationary ball on top of a hill Kinetic Kinetic and Potential Potential energy can be interconverted 3
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4 First Law of Thermodynamics: First Law of Thermodynamics: The total energy of the universe is constant. Joseph Black James Watt Benjamin Thompson Robert Mayer James Joule
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A state function is a property of a system that can be defined by the current state of the system and is INDEPENDENT of the pathway by which that state was achieved. e.g. energy, pressure, volume, temperature are state functions Both hikers have experienced the same net increase in potential energy independent of their paths of ascent. 5
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Changes in State are represented by “ ”: V, P, E E = E final - E initial A change in the energy of a system, E, depends ONLY upon the initial and final energies of the system. It is INDEPENDENT of the pathway by which that change occurred. (It is a state function). 6
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Energy flowing into a system E >0 Energy flowing out of a system E<0 Universe = System + Surroundings Chemists evaluate energy changes from the perspective of the system: 7
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Internal Energy of the System (U) The internal energy internal energy of a system system is the sum of the kinetic and potential energies in the system. For atoms and molecules in chemical reactions: Kinetic energy Kinetic energy – molecular or atomic motion, movement of electrons Potential energy Potential energy – attractive or repulsive interactions between electrons, nuclei, atoms, and molecules. Total internal energy cannot be measured but
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CHM1311 - Lecture(7) - Thermochemistry Thermochemistry The...

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