Calculate the change in Gibbs free energy for each of the sets of ? H rxn, ? S r

Question

Calculate the change in Gibbs free energy for each of the sets of ?Hrxn, ?Srxn, and T given in the following problem.

Part A

?H?rxn=? 87 kJ , ?Srxn=? 154 J/K , T= 308 K

Express your answer using two significant figures.

Part B

?H?rxn=? 87 kJ , ?Srxn=? 154 J/K , T= 751 K

Express your answer using two significant figures.

Part C

?H?rxn= 87 kJ , ?Srxn=? 154 J/K , T= 308 K

Express your answer using three significant figures.

Part D

?H?rxn=? 87 kJ , ?Srxn= 154 J/K , T= 407 K

Express your answer using three significant figures.

Part E

Predict whether or not the reaction in part A will be spontaneous at the temperature indicated. (Assume that all reactants and products are in their standard states.)

Part F

Predict whether or not the reaction in part B will be spontaneous at the temperature indicated. (Assume that all reactants and products are in their standard states.)

Part G

Predict whether or not the reaction in part C will be spontaneous at the temperature indicated. (Assume that all reactants and products are in their standard states.)

Part H

Predict whether or not the reaction in part D will be spontaneous at the temperature indicated. (Assume that all reactants and products are in their standard states.)

Explanation / Answer

A)
?Ho = -87.0 KJ/mol
?So = -154 J/mol.K
= -0.154 KJ/mol.K
T = 308 K

use:
?Go = ?Ho - T*?So
?Go = -87.0 - 308.0 * -0.154
?Go = -39.568 KJ/mol
Answer: -40. KJ/mol

B)
?Ho = -87.0 KJ/mol
?So = -154 J/mol.K
= -0.154 KJ/mol.K
T = 751 K

use:
?Go = ?Ho - T*?So
?Go = -87.0 - 751.0 * -0.154
?Go = 28.654 KJ/mol
Answer: 29 KJ/mol

C)
?Ho = 87.0 KJ/mol
?So = -154 J/mol.K
= -0.154 KJ/mol.K
T = 308 K

use:
?Go = ?Ho - T*?So
?Go = 87.0 - 308.0 * -0.154
?Go = 134.432 KJ/mol
Answer: 134 KJ/mol

D)
?Ho = -87.0 KJ/mol
?So = 154 J/mol.K
= 0.154 KJ/mol.K
T = 407 K

use:
?Go = ?Ho - T*?So
?Go = -87.0 - 407.0 * 0.154
?Go = -149.678 KJ/mol
Answer: -150. KJ/mol

E)
since ?Go is negative, it is spontaneous

F)
since ?Go is positive, it is non spontaneous

G)
since ?Go is positive, it is non spontaneous

H)
since ?Go is negative, it is spontaneous

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