Predict which of the following reactions would proceed spontaneously at `298K?`

Options

A. `Co(s)+Fe^(2+)(aq)rarrCo^(2+)(aq)+Fe(s) `
`E^(c-)._(Co^(2+)//Co)=-0.28V`
B. `Cd^(2+)(aq)+Fe(s)rarrCd(s)+Fe^(2+)(aq) `
`E^(c-)._(Cd^(2+)//Cd)=-0.4V`
C. `Cd(s)+Co^(2+)(aq)rarr Cd^(2+)(aq)+Co(s)`
`E^(c-)._(Fe^(2+)//Fe)=-0.44V`
D. `Zn^(2+)(aq)+H_(2)rarr Zn(s)+2H^(o+)`
`E^(c-)._(Zn^(2+)//Zn)=-0.76V`

Answer

b,c

Explanation

`E^(c-)._(Co^(2+)|Co)=-0.28V,E^(c-)._(Cd^(2+)|Cd)=-0.4V,`
`E^(c-)._(Fe^(2+)|Fe)=-0.44V, E^(c-)._(Zn^(2+)|Zn)=-0.76V,E^(c-)._(H^(o+)|H_(2))=0V`
Using`: E^(c-)._(cell)=(E^(c-)._(reduction))_(cathode)-(E^(c-)._(reduction))_(anode)`
`a. E^(c-)._(cell)=-0.44-(-0.28)=-0.16V`
`b. E^(c-)._(cell)=-0.4-(-0.44)=+0.04V`
`c. E^(c-)._(cell)=-0.28-(-0.4)=0.12V`
`d. E^(c-)._(cell)=(=0.76)-0=-0.76V`