Calculate dG, dA, and dSuniv for each of the following 1. Melting two moles of i

Question

Calculate dG, dA, and dSuniv for each of the following
1.  Melting two moles of ice at 0C and 1atm.  density of water = 1 g/cm^3  density of ice = .917g/cm^3

2. Evaporation of 1 mole of benzene at its normal boiling point (80.1C) and 1atm

3. Adiabatic expansion of 1 mole of an ideal gas into a vacuum.  Ti = 300K  Vi=2L Vf=6L . Calculate dG, dA, and dSuniv for each of the following
1.  Melting two moles of ice at 0C and 1atm.  density of water = 1 g/cm^3  density of ice = .917g/cm^3

2. Evaporation of 1 mole of benzene at its normal boiling point (80.1C) and 1atm

3. Adiabatic expansion of 1 mole of an ideal gas into a vacuum.  Ti = 300K  Vi=2L Vf=6L .

Explanation / Answer

1. At the melting point, liquid is in equilibrium with the solid. That means that the free energy change for the reaction:

H2O(s) -> H2O(L)

is equal to zero.

?G = 0 = ?H - T*?S

?S = ?H/T

For this reaction, ?H is simply the enthalpy of fusion and T = 273K, so:

?S_fusion = (6010J/mol)/(273K) = 22.02 J/(K*mol)

If 1 mole of water melts, then the entropy change of the water is 22.02 J/K.

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