A combustion reaction releases 783 kJ of energy at 25degree C. Calculate the cha

Question

A combustion reaction releases 783 kJ of energy at 25degree C. Calculate the change in entropy of the surroundings, delta S_surr. Calculate the change in entropy if the reaction is done at 400degree C. A reaction at a high temperature has a negative value for enthalpy and a negative value for entropy. Is this reaction spontaneous or nonspontaneous? What about at a low temperature? Consider the following information A + B rightarrow C delta H = -40.5 kJ delta S = 342.1 j/K 40 degree C Just by looking at the signs of the values for entropy and enthalpy, is this reaction spontaneous or nonspontaneous? Calculate the change in free energy of the reaction, delta G. ls there a temperature where the reaction will reverse in spontaneity? Use the standard entropy values (delta S_f degree) in the Appendix to solve for delta S degree of each reaction at 25degree C. Solve for delta G degree_rxn for both reactions as well using the standard free energy values. (delta G_f degree) delta H degree = 180.7 kJ; delta S degree = 24.7J/K 25degree C Calculate the standard free-energy change for the reaction at 25degree C. Calculate delta G at 500 degree C using the delta G degree value calculated from part a. (Hess' Law) delta G degree = +1102 What is the change in free energy when 18 moles of chlorine gas are reacted with phosphorus to make phosphorus trichloride.

Explanation / Answer

1) Ssystem = qrev/T

Ssystem = (783 KJ / 298 K) = -2.868 KJ /K

Ssystem = - Ssurrounding =-2.868 KJ /K = -2868 J/K

b) Ssystem = qrev/T

Ssystem = (783 KJ / 673 K ) = 1.163 KJ/K = 1163 J/K

Ssurrounding =-1163 J/K

2) G = H - TS

spontaneous if G < 0

nonspontaneous if G > 0

G = -H + TS at high temperature reaction will nonspontaneous

at low temperature reaction will spontaneous

3) G = -40500 J - ( 313 K ) (342.1 J/K)

G = -147577.3 J

reaction is spontaneous

temperature will negetive for spontenity

4)

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