First Law of Thermodynamics

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First Law of Thermodynamics
Work: Total energy transferred to a system by macroscopic forces exerted on it by other systems Work done by a gas on a piston A Work done by a fluid as it expands from V0 to Vf Fluid (gas) F =P A x x Energy leaves the system x A Energy feed in the system

 Q A First law of thermodynamics:
All systems have an internal energy state function that is changed by heat transferred to or from the system and by the work done by or on the system. nothing but conservation of energy closed system internal energy state function Energy transferred by macroscopic mechanical means Energy transferred by non-macroscopic mechanical means A Q

Joule’s experiment: the mechanical equivalent of heat
What do we learn from the experiment 1 -dissipative work Wdis done -no heat flow Q -change in measured by change in temperature (V=const.) 2 -same change in could be created by a heat flow Q Joule's Paddle-Wheel Apparatus 1849 Change of internal energy U in a dissipative process is the same as if there had been a heat flow Q into the system of equal magnitude to Wd. click for virtual experiment

Application of 1. law in a free expansion experiment
V1 ,Ts V2 ,Tf Thermal insulation gas no heat flow =:adiabatic process fixed walls no work done by the container W=0 1. law: ideal gas U=U(T) for the ideal gas only

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