A) When will the following two reactions both be spontaneous? Reaction A: ?H = ?

Question

A) When will the following two reactions both be spontaneous?

Reaction A: ?H = ?100 kJ, ?S = +100 J/K                   Reaction B: ?H = ?100 kJ, ?S = ?100 J/K                  

A) All temperatures

B) No temperatures

C) Temperatures above 1000 K

D) Temperatures below 1000 K

E) At 1000 K only

B) Which of the following statements is true for the spontaneous coupled reaction?

ATP + H2O à ADP + Pi           ?G° = ?31 kJ/mol;                    PEP + H2O à Pyr + Pi             ?G° = ?62 kJ/mol.

A) The conversion of ATP to ADP drives the conversion of PEP to Pyr

B) The conversion of ATP to ADP drives the conversion of Pyr to PEP

C) The conversion of PEP to Pyr drives the conversion of ATP to ADP

D) The conversion of PEP to Pyr drives the conversion of ADP to ATP

E) None of the above statements are true

C) For the following reaction, what is the maximum percent of heat that can be converted into useful work at 150°C?

H2(g) + ½ O2(g) à H2O(g) ?H° = ?241.8 kJ/mol, ?S° = ?44.5 J/mol?K

A) 64%                         

B) 78%                         

C) 82%                          

D) 92%                         

E) 98%                         

D) A saturated solution of PbCl2 at 25°C contains 0.032 M Cl? ions. From this information, estimate the ?G°rxn for the dissolution of lead (II) chloride at 25°C.

A) 17 kJ/mol       

B) 20 kJ/mol       

C) 27 kJ/mol       

D) 32 kJ/mol       

E) 35 kJ/mol

Explanation / Answer

1. ?G = ?H - T ?S

For a reaction to be spontaneous , the ?G must be negative.

As in the given data of the reactions the ?S is positive , then reaction will be spontaneous for all temperatures .

So option A is correct .

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