P21_003

# P21_003 - E int = Q − W . Now the internal energy of an...

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3. (a) Since the gas is ideal, its pressure p is given in terms of the number of moles n ,thevo lume V ,and the temperature T by p = nRT/V . The work done by the gas during the isothermal expansion is W = Z V 2 V 1 pdV = nRT Z V 2 V 1 dV V = nRT ln V 2 V 1 . We substitute V 2 =2 V 1 to obtain W = nRT ln 2 = (4 . 00 mol) µ 8 . 31 J mol · K (400 K) ln2 = 9 . 22 × 10 3 J . (b) Since the expansion is isothermal, the change in entropy is given by ∆ S = R (1 /T ) dQ = Q/T , where Q
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Unformatted text preview: E int = Q − W . Now the internal energy of an ideal gas depends only on the temperature and not on the pressure and volume. Since the expansion is isothermal, ∆ E int = 0 and Q = W . Thus, ∆ S = W T = 9 . 22 × 10 3 J 400 K = 23 . 1 J / K . (c) ∆ S = 0 for all reversible adiabatic processes....
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## This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.

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