What is the normal melting point, in degree Celsius, for naphthalene, C_10H_8, (

Question

What is the normal melting point, in degree Celsius, for naphthalene, C_10H_8, (i.e., the temperature at which C_10H_8(s) and C_10H_8(l) are in equilibrium at 1 atm pressure)? For the phase change change C_10H_8(s) rightarrow C_10H_8(l) under the standard conditions, Delta H degree_fusion = 19.1 kJ/mol and Delta S degree_fusion = 47.6 J/(K. mol). 1.401 degree Celsius 2. -128 degree Celsius 3. 0.401 degree Celsius 4. 128 degree Celsius 5. -401 degree Celsius For each of the following processes, predict the entropy change Delta S (indicate > 0 or

Explanation / Answer

5) Melting point of Naphthalene T = Hofusion/Sofusion

   = 19.1 kJ/mol / 47.6 J/K/mol

= 19100 / 47.6 K

= 401 K

= 401 - 273 oC

= 128 oC

6) order of entropy :

gas > liquid > solid

a) 2 moles of gas --------> 3 moles of gas

No of gas molecules increases.

Entropy increases.

Hence,

  S > 0

b) g + l -----> aq

   entropy decreases.

S < 0

c) s + g ------> s

  entropy decreases.

S < 0

d) g + l -------> g + g

More no of gas molecules on the product side.

Entropy increases.

  S > 0

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