Calculate& values for the following cells. Which reactions are spontaneous as wr

Question

Calculate& values for the following cells. Which reactions are spontaneous as written (under standard conditions)? Balance the equations. Standard reduct potentials are found in the Standard Reduction Potentials table. (Use the lowest possible coefficients. Include states-of-matter under the given conditions in answer.) (a) (a) Cr2072 (aq)I (aq) I2(s) Cr3+(aq) Cr2072-(aq) + 1-(aq) 12(s) + C (aq) spontaneity: spontaneous O not spontaneous balanced equation: chemPad Help Greek Cr2072-(aq) + F-(aq)-F2(g) + Cp3+(aq) (b) 8o spontaneity spontaneous O not spontaneous

Explanation / Answer

ANSWER

Cr2O72- + I- -------> I2 + Cr3+

Balance Cr2O72- + 2I- + 8H+-------> I2 + 2Cr3+ + 4H2O

I- is oxidised and Cr2O72- is reduced.

Eo = Er - El = 1.33 - 0.535 = 0.795V

Er = standard reduction potentia of reduced specie and

El = standard reduction potential of oxidised specie

Since Eo is positive the reaction is SPONTANEOUS.

(b) Cr2O72- + F- -------> F2 + Cr3+

Balanced

Cr2O72- + 2F- + 8H+-------> F2 + 2Cr3+  + 4H2O

Eo = Er - El = 1.33 - 2.87 = - 1.54V

Since Eo is negative the reaction is NON SPONTANEOUS

(c) H2 -----> H+(aq) + H- (aq)

reaction is balanced

Hydrogen is getting reduced as well as oxidised. Reduction potential of both the reactions is 0V

Eo = 0-0 = 0V

Non spontaneous reactipn

(d) Cd+2 + Zn(s) ----> Zn+2 + Cd(s)

Reaction is balanced

Cd+2 is reduced and Zn is oxidised

Eo = Er - El = - 0.403 - (-0.763) = + 0.36V

Reaction is spontaneous.

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