Phys-4420 thermodynamics & statistical mechanics spring 2006




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PHYS-4420 THERMODYNAMICS & STATISTICAL MECHANICS SPRING 2006
Class Activity - Class 3 January 24, 2006

Name________ANSWERS________________ __


When a system is taken from state i to state f along path iaf in the figure, Q = 50 cal and W = 20 cal. Along path ibf, Q = 36 cal.

a) What is W along path ibf ?


Along path iaf, U = Q – W = 50 cal 20 cal = 30 cal

Along path ibf, U is the same. Therefore, for path ibf



W = Q – U = 36 cal 30 cal W = 6 cal
b) If W = – 13 cal for the curved return path fi, what is Q for this path?
Along path fi, U = 30 cal. Therefore, for path fi,

Q = W + U = – 13 cal 30 cal Q = 43 cal

c) Take Ui = 10 cal. What is Uf ?


Uf = Ui + U = 10 cal + 30 cal Uf = 40 cal

d) If Ub = 22 cal, what are the values of Q for path ib and bf ?


Wibf = Wib + Wbf = 6 cal, but Wbf = 0, so Wib = 6 cal.

For ib, Qib = Wib + Uib = 6 cal + 22 cal – 10 cal Qib = 18 cal


For bf, Qbf = Wbf + Ubf = 0 + 40 cal – 22 cal Qbf = 18 cal


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