Chp3_FirstLaw

# Chp3_FirstLaw - First Law Introduction to Terms The First...

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First Law – Introduction to Terms: The First Law of thermodynamics can be expressed in either of two equivalent forms, both of which convey the essential nature of the law, to wit: conservation of energy in an isolated system ( aka universe). 0 = + = + = w q E E E surr sys univ The subscripts refer to “universe”, “system”, and “surroundings” respectively. Let us examine each term. Delta E ( E): Denotes the change in internal energy during a chemical/physical process. Units of Joules (J). The capital letter denotes that the internal energy is a “state function”. This means that the change in internal energy (like potential energy) depends only on the initial and final states of the process (e.g. reactants and products). That is, i f E E E - = . In other words, one simply subtracts the internal energy of the initial state from that of the final state to obtain the change. For those with interest in mathematics, this is related to exact differentials: ) ( ) ( ) ( 1 2 2 1 x F x F x dxf x x - = where F(x) is the anti-derivative of f(x). That is to say, the integral is “replaced” by a function evaluation at the endpoints (the function being the

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Chp3_FirstLaw - First Law Introduction to Terms The First...

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