The_First_Law

# The_First_Law - The First Law of Thermodynamics Definitions...

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1 The First Law of Thermodynamics Definitions system isolated system open system closed system properties state of a system change in state path process cycle – cyclic process state variable – state function Each time you have a problem to solve in Thermodynamics you should pose the following questions to yourself: what is the system? where is the boundary? what is the initial state? what is the final state? what is the path of the transformation? Work and Heat work any quantity that flows across the boundary of a system during a change in its state and is completely convertible into the lifting of a mass in the surroundings Note that in this thermodynamic definition of work: a. work appears only at the boundary of the system; b. work appears only during a change in system; c. work is manifested by an effect in the surroundings; d. work is an algebraic quantity ( it can be calculated from the change in PE of the mass, E potential = mgh) e. W < 0, the height of the mass in the surroundings is lifted: work has been done by the system on the surroundings. W > 0, the height of the mass in the surroundings is lowered. Work has been done on the system by the surroundings.

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2 Heat a quantity that flows across the boundary of a system during a change in state by virtue of a difference in temperature between the system and its surroundings and flows from a point of higher to a point of lower temperature Note that in this thermodynamic definition of heat: a. heat appears only at the boundary of the system; b. heat appears only during a change in state; c. the quantity of heat is manifested by an effect in the surroundings; d. the quantity of heat is equal to the number of grams of water in the surroundings which are increased by one degree in temperature starting at a specified temperature under a specified pressure; e. heat is an algebraic quantity. Heat is positive if a mass of water in the surroundings is cooled, in which case heat has flowed from the surroundings to the system.
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## The_First_Law - The First Law of Thermodynamics Definitions...

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