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Based on the reduction potentials listed in the textbook appendix, which of the following redox reactions do you expect to occur spontaneously?  

W. 2Al(s)+3Pb2+ (aq) → 2Al3+ (aq)+3Pb(s)  
X. Fe(s)+Cr3+ (aq) → Fe3+ (aq)+Cr(s)  
Y. Ca2+ (aq)+Zn(s) → Ca(s)+Zn2+(aq)  
Z. 2Cu+(aq)+Co(s) → 2Cu(s)+Co2+ (s)

a. W only
b. X, Y and Z
c. Y only
d. X and Z
e. Z only
f. X and Y
g. W, X and Z
h. X and Y
i.W and Z

User Vedanshu
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1 Answer

7 votes

Answer: The redox reactions that occur spontaneously are Reaction W and Reaction Z.

Step-by-step explanation:

For the reaction to be spontaneous, the Gibbs free energy of the reaction must come out to be negative.

Relationship between standard Gibbs free energy and standard electrode potential follows:


\Delta G^o=-nFE^o_(cell)

For a reaction to be spontaneous, the standard electrode potential must be positive.

To calculate the
E^o_(cell) of the reaction, we use the equation:


E^o_(cell)=E^o_(cathode)-E^o_(anode) .......(1)

Substance getting oxidized always act as anode and the one getting reduced always act as cathode.

  • For reaction W:

The chemical reaction follows:


2Al(s)+3Pb^(2+)(aq.)\rightarrow 2Al^(3+)(aq.)+3Pb(s)

We know that:


E^o_(Al^(3+)/Al)=-1.66V\\E^o_(Pb^(2+)/Pb)=-0.13V

Calculating the
E^o_(cell) using equation 1, we get:


E^o_(cell)=-0.13-(-1.66)=1.53V

As, the standard electrode potential is coming out to be positive. So, the reaction is spontaneous.

  • For reaction X:

The chemical reaction follows:


Fe(s)+Cr^(3+)(aq.)\rightarrow Fe^(3+)(aq.)+Cr(s)

We know that:


E^o_(Fe^(3+)/Fe)=0.77V\\E^o_(Cr^(3+)/Cr)=-0.74V

Calculating the
E^o_(cell) using equation 1, we get:


E^o_(cell)=-0.74-(0.77)=-1.51V

As, the standard electrode potential is coming out to be negative. So, the reaction is not spontaneous.

  • For reaction Y:

The chemical reaction follows:


Zn(s)+Ca^(2+)(aq.)\rightarrow Zn^(2+)(aq.)+Ca(s)

We know that:


E^o_(Ca^(2+)/Ca)=-2.87V\\E^o_(Zn^(2+)/Zn)=-0.76V

Calculating the
E^o_(cell) using equation 1, we get:


E^o_(cell)=-2.87-(-0.76)=-2.11V

As, the standard electrode potential is coming out to be negative. So, the reaction is not spontaneous.

  • For reaction Z:

The chemical reaction follows:


Co(s)+2Cu^(+)(aq.)\rightarrow Co^(2+)(aq.)+2Cu(s)

We know that:


E^o_(Cu^(+)/Cu)=0.34V\\E^o_(Co^(2+)/Co)=-0.28V

Calculating the
E^o_(cell) using equation 1, we get:


E^o_(cell)=0.34-(-0.28)=0.62V

As, the standard electrode potential is coming out to be positive. So, the reaction is spontaneous.

Hence, the redox reactions that occur spontaneously are Reaction W and Reaction Z.

User Francesco Vadicamo
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8.7k points