The half-reaction at the cathode in an electrochemical cell is given below. What other half-reaction would most likely occur at the anode to produce a
spontaneous reaction?
Zn2+ (aq) + 2e →
Zn(s)

A. H2(g) → 2H+(aq) + 2e
B. Zn(s)
Zn2+ (aq) + 2e
C. K*(aq) + e
-
K(s)
D. Al(s) → A13+(aq) + 3e
SUM

Explanation:

a) Anode:  

Cathode :  

b)  

c) As  , the reaction is spontaneous.

d)  

Explanation:

a) Here Ni undergoes oxidation by loss of electrons, thus act as anode. Hydrogen undergoes reduction by gain of electrons and thus act as cathode.

Anode:  

Cathode :  

b) The representation is given by writing the anode on left hand side followed by its ion with its molar concentration. It is followed by a slat bridge. Then the cathodic ion with its molar concentration is written and then the cathode.

c)  

Where both  are standard reduction potentials.

= +ve, reaction is spontaneous

= -ve, reaction is non spontaneous

= 0, reaction is in equilibrium

Thus as  , the reaction is spontaneous.

d) The standard emf of a cell is related to Gibbs free energy by following relation:

= standard gibbs free energy

n= no of electrons gained or lost

F= faraday's constant

= standard emf

Thus value of Gibbs free energy is -48250 Joules.

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms