JAMB Chemistry Past Questions & Answers

1,956.

When sugar is dissolved in tea, the reaction is always accomplished by

positive change

negative entropy change

no entropy change

a minimum entropy change

Correct answer is A

The dissolution of sugar in tea is accompanied by positive change in entropy. When there is a change in the state of a substance from solid to liquid, there is an increase in entropy. In general, if a substance changes its structure from a condensed state to a less condensed state, then we say there is an increase in entropy.

1,957.

CO_(g) + H₂O_(g) → CO_2(g) + H_2(g)
From the reaction above, calculate the standard enthalpies of formation of CO_2(g), H₂O_(g) and CO_(g) in kJ mol^-1 are -394, -242, and -110 respectively.

-262 kJ mol^-1

-42 kJ mol^-1

+42 kJ mol^-1

+262 kJ mol^-1

View answer & explanation

Correct answer is B

CO + H₂O → CO₂ + H₂ DH = 394 kJ mol^-1
-242 + 110 = -352 kJ mol^-1
35 = -394 -(352)
= -394 + 352
= -42 kJ mol^-1

1,958.

In the electrolysis of a concentrated solution of sodium chloride using electrodes, which of the following ions are discharged at the cathode and anode respectively?

Na⁺ and Cl^-

Na⁺ and OH^-

H⁺ and OH^-

H⁺ and Cl^-

View answer & explanation

Correct answer is D

In the electrolysis of conc. NaCl,

anions = \(Cl^- and OH^-\)

cations = \(H^+ and Na^+\)

So, hydrogen ion will migrate to the cathode, and Cl ion will migrate to the anode at the expense of hydroxide ion because of higher concentration in the solution

1,959.

When at equilibrium, which of the reactions below will shift to the right if the pressure is increased and the temperature is kept constant?

2SO_3(g) ↔ 2SO_2(g) + O_2(g)

2CO_2(g) ↔ 2CO_(g) + O_2(g)

2H_2(g) + O_2(g) ↔ 2H₂O_(g)

2NO_(g) ↔ N_2(g) + O_2(g)

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

1,960.

If y is an oxidizing agent that reacts with a reducing agent, Z, which of the following is correct?

Y increases in oxidation number