Consider the process H2O l to H2O g at 400K and 1 bar Calcul

Consider the process:

H₂O (l) to H₂O (g) at 400K and 1 bar.

Calculate the following. In doing so, you m ay assume relevant heat capacities are temperature independent, but you may NOT assume changes in entropy or enthalpy are temperature independent. You may use the data below:

Standard enthalpy of formation of H₂O (l) is -285.83 kJ/mol and H₂O (g) is -241.82 kJ/mol at 25 celsius

Standard entropies for H₂O liquid and gas are 69.91 J K^-1mol^-1 and 188.72 J K^-1 mol^-1 at 25 celsius respectively

The free energies of formation of H₂O liquid and gas are -237.18 kJ/mol and -228.59 kJ/mol at 25 celsius respectively

The constant pressure molar heat capacities (c_p) for the liquid and gas are 75.29 J K^-1 mol^-1 and 35.58 J K^-1 mol^-1 respectively

a) Calculate delta H for the process

b) Calculate delta S for the process

c) Calculate delta G for the process

d) Is it spontaneous?

Solution

H2O (l) -----> H2O (g)

dH rxn = dH products - dH reactants

dH rxn = -241.82 -(-285.83)

dH rxn = 44.01 kJ

dS rxn = dS products - dS reactants

dS rxn = 188.72 - 69.91

dS rxn = 118.81 J/K mol

dG rxn = dG products - dG reactants

dG rxn = -228.59 - (-237.18)

dG rxn = 8.59 kJ/mol

since dG = +ve so the reactiion is not spontaneous reaction.

dG = dH - Tds

for spontaneous reaction dG = -ve so that we must get dH = -ve and TdS = +ve, then only the reaction will become spontaneous.