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9.1 Thermo

9.1 Thermo - Heat and Work First Law of Thermodynamics 9.1...

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1 First Law of Thermodynamics 9.1 Heat and Work Thermodynamic Processes Heat and Work Heat Work Thermodynamics is the science of heat and work Heat is a form of energy Mechanical work done on a system produces a rise in temperature like heat added to the system. Calorimetry Mechanical equivalent of heat 1calorie =4.184 J Work Heat input Q Heat input into a system can produce work W F x = W PA x P V = = For the case of thermal expansion work is done by the system. First Law of Thermodynamics The change in the internal energy of a system U, is equal to the heat input Q minus the work done by the system. Internal Energy U System Heat Q Work W U Q W = The internal energy is the energy stored in the system. For an ideal gas the internal energy is the kinetic energy of the gas

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2 Thermodynamic processes in an ideal gas The state of the ideal gas is determined by the three parameters, PVT. A thermodynamic process is the transition between states with input or output of heat and work with changes in internal energy. The internal energy U is a property of the state. U determined by the initial and final state and is independent of path The heat absorbed and work done in the process depend on the path. U 1 U 2 State 1 (P 1 , V 1 , T 1 ) State 2 (P 2 , V 2 , T 2 ) PV diagram P V Each point in the diagram represents a State of the system The temperature T is not plotted but is not an independent variable. T can be calculated from P and V using the ideal gas law. The points of constant temperature on the PV diagram are hyperbola State 1 State 2 nRT P V = For constant T T 1 T 2 Thermodynamic processes P V State 1 (T 1 , P 1 , V 1 ) x State 2 (T 2 , P 2 , V
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9.1 Thermo - Heat and Work First Law of Thermodynamics 9.1...

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