Question

(28.1) Let’s reconsider the 23.5 kg of silver that we warmed and then melted in PS#14. (a) In warming the silver its entropy [Choose One:] increased remained constant decreased . (b) In melting the silver its entropy [Choose One:] increased remained constant decreased . (c) By what amount did the entropy of the silver change while it was melting? [The latent heat of fusion for Ag is 88 kJ/kg and it melts at TAg = 961 C.] (28.2) A sample of water with mass M = 25 g with initial temperature Ti = 15 C comes fresh from your tap and into a slot in an icecube tray. The water is put into the the freezer and eventually turns to ice. (a) In cooling the water to 0 C [the temperature at which it begins to freeze] its entropy [Choose One:] increased remained constant decreased . (b) In solidifying the water its entropy [Choose One:] increased remained constant decreased . (c) By what amount did the entropy of the water sample change while it was freezing? [The latent heat of fusion for water is 333 kJ/kg and it freezes at 0 C.]

Answer #1

28.1)

a) In warming the silver its entropy
**increased**

b) In melting the silver its entropy
**increassed**

c) change in entropy, delta_S = delta_Q/T

= m*Lf/T

= 23.5*88*10^3/(961 + 273) (Temperature must be in Kelvin)

= **1676 J/K
<<<<<<<<<--------------------Answer**

28.2)

a) In cooling the water to 0 C [the temperature at which it
begins to freeze] its entropy **decreased**

b) In solidifying the water its entropy
**decreased.**

c) change in entropy, delta_S = -Q/T

= -m*Lf/T

= -25*333*10^3/(0 + 273)

= **-30494 J
<<<<<<<<<--------------------Answer**

here negative indicates decrease in entropy.

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