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FIRST LAW OF THERMODYNAMICS

Energy Conservation

Question 1

First law of Thermodynamics is a consequence Conservation of Energy

Statement of First Law (∆Q = ∆U + ∆W)

The energy (∆Q) supplied to the system goes in partly to increase the  energy of the system (∆U) and the rest in on the environment (∆W).

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More about Internal Energy U

Question

Internal Energy  (∆U = ∆Q – ∆W)  is a macroscopic state variable.  Suppose a system change the state from initial to final. Identify the wrong statement

Answers

Heat supplied to the system by the surroundings ∆Q depends on the path taken to go from the initial to final states

Work done by the system on the surroundings ∆W depends on the path taken to go from the initial to final states

The combination (∆Q – ∆W) depends on the path taken to go from the initial to final states

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Work done by the system against a constant Pressure P

Consider a system fitted with movable piston ( ie constant P), with area of cross section (A). During the Thermodynamic process, system does a work (∆W) and the piston gets displaced by ∆x

Force = x Area

Work = x Displacement

Work = Pressure x x Displacement

or  W = P ∆V

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