Determine which of the following pairs of reactants will result in a spontaneous reaction at 25°c. none of the above pairs will react. fe3+(aq) + mg(s) pb2+(aq) + au(s) ag+(aq) + br⁻(aq) li+(aq) + cr(s)

Only gives spontaneous reaction.

Explanation:

A redox reaction will be spontaneous if standard reduction potential () of the reaction is positive. Because it leads to negative standard gibbs free energy change (), which is a thermodynamic condition for spontaneity of a reaction.

Where and represents standard reduction potential of reduction half cell and standard reduction potential of oxidation half cell.

(1) Oxidation:         ;  

Reduction:         ;

So,

Hence this pair will give spontaneous reaction.

(2) Similarly as above,

Hence this pair will give non-spontaneous reaction.

(3) Similarly as above,

Hence this pair will give non-spontaneous reaction.

(4)  Similarly as above,

Hence this pair will give non-spontaneous reaction.

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