Be sure to answer all parts. the standard enthalpy of formation and the standard entropy of gaseous benzene are 82.93 kj/mol and 269.2 j/k·mol, respectively. calculate δh o , δs o , and δg o for the following process at 25.00°c. c6h6(l) → c6h6(g) δh o = kj/mol δs o = j/k·mol δg o = kj/mol is the reaction spontaneous at 25.00°c?

The reaction is not spontaneous at 25.00°C

Gibbs free energy is the maximum possible work given by chemical reactions at constant pressure and temperature. Gibbs free energy can be used to determine the spontaneity of a reaction

If the Gibbs free energy value is <0 (negative) then the chemical reaction occurs spontaneously. If the change in free energy is zero, then the chemical reaction is at equilibrium, if it is> 0, the process is not spontaneous

Free energy of reaction (G) is the sum of its enthalpy (H) plus the product of the temperature and the entropy (S) of the system

Can be formulated: (at any temperature)

or at (25 Celsius / 298 K, 1 atm = standard)

ΔG ° reaction = ΔG ° f (products) - ΔG ° f (reactants)

Under standard conditions:

The value of °H ° can be calculated from the change in enthalpy of standard formation:

∆H ° (reaction) = ∑Hf ° (product) - ∑ Hf ° (reagent)

The value of ΔS ° can be calculated from standard entropy data

∆S ° (reaction) = ∑S ° (product) - ∑ S ° (reagent)

We complete the existing data from the reaction

C6H6 (l) → C6H6 (g)

∑Hf ° C6H6 (l): 49.04 kJ mol⁻¹

∑ Hf ° C6H6 (g): 82.93kJ mol⁻¹

∑S ° [C6H6 (l)]: 172.8 J mol⁻¹

∑S ° [C6H6 (g)]: 269.2 J mol⁻¹

so that:

∆H ° (reaction) = ∑ Hf ° C6H6 (g) -∑Hf ° C6H6 (l)

∆H ° (reaction) = 82.93kJ mol⁻¹ - 49.04 kJ mol⁻¹

∆H ° (reaction) = 33.89kJ mol⁻¹

∆S ° (reaction) = ∑S ° [C6H6 (g)] - ∑S ° [C6H6 (l)]

∆S ° (reaction) = 269.2J mol⁻¹ - 172.8 J mol⁻¹

∆S ° (reaction) = 96.4 J mol⁻¹ = 96.4 .10-3 kJ mol⁻¹

∆G ° at 298 K

∆G ° = ∆H ° - T∆S °

∆G ° = 33.89kJ mol⁻¹ - 298.96.4 .10-3 kJ mol⁻¹

∆G ° = 5.16 kJ mol⁻¹

Because the value of ∆G ° is positive, the reaction is not spontaneous

Delta H solution  

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an exothermic reaction  

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as endothermic or exothermic  

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an exothermic dissolving process  

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Keywords: the standard gibbs free energy of formation,nonspontaneous

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