JAMB Chemistry Past Questions & Answers - Page 361

1,801.

Zinc and carbon rods are used as anode and cathode respectively in a

A.

Leclanche cell

B.

lead accumulator

C.

Daniel cell

D.

voltaic cell

Correct answer is A

In a Leclanche cell, the anode and the cathode are a zinc rod and a carbon rod respectively. The electrolyte is an ammonium chloride solution or paste (wet or dry cell).

1,802.

H2(g) + Br2(g) → 2HBr(g)
The above reaction is carried out at 25oC. ΔH is -72 kJ mol-1 and ΔS is - 106 J mol-1K-1, the reaction will?

A.

not proceed spontaneously at the given

B.

proceed spontaneously at the given temperature

C.

proceed in the reverse direction at the given temperature

D.

proceed spontenously at lower temperature

Correct answer is B

 Where ∆G = ∆H - T∆S

Given data; ∆G = ?

∆H = -72KJ/mol, 

T→ (25+273)K = 298K

∆S = -106J/mol or -0.106KJ/mol/K

: ∆G = -72 -(298 * -0.106)

= -72 + 31.588

∆G = -40.412KJ/mol

One of the condition for spontaneity of a reaction as ∆G to be negative.

1,803.

Trioxonitrate (V) acid is not used for preparing hydrogen gas from metals because it

A.

is strongly oxidizing

B.

is volatile

C.

renders the metal passive

D.

forms a layer of oxide on the metal

Correct answer is A

No explanation has been provided for this answer.

1,804.

The ion that can be used as an oxidizing agent is

A.

Au3+

B.

Fe3+

C.

ClO-

D.

Ca2+

Correct answer is C

No explanation has been provided for this answer.