Question

Which of the following chemical reactions has positive entropy change?
A. N2(g) + 3 H2(g) \longrightarrow ⟶ 2NH3(g)
B. Br2(g) \longrightarrow ⟶ Br2(l) N2O4(g)
C. \longrightarrow ⟶ 2 NO2(g)
D. NaOH(aq) + CO2(g) \longrightarrow ⟶ NaHCO3(aq)

Answer 1

Answer: $N_2O_4(g)\longrightarrow 2NO_2(g)$

Explanation:

Entropy is the measure of randomness or disorder of a system. If a system moves from  an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.

$\Delta S$ is positive when randomness increases and $\Delta S$ is negative when randomness decreases.

a) $N_2(g)+3H_2(g)\longrightarrow 2NH_3(g)$

4 moles of gas are converting to moles of gas, hence the entropy decreases.

b) $Br_2(g)\longrightarrow Br_2(l)$

1 mole of gas is converting to 1 mole of liquid, hence the entropy decreases.

c) $N_2O_4(g)\longrightarrow 2NO_2(g)$

1 mole of gas is converting to 2 moles of gas, hence the entropy increases.

d) $NaOH(aq)+CO_2(g)\longrightarrow NaHCO_3(aq)$

1 mole of gas is disappearing , hence the entropy decreases.

Thus $N_2O_4(g)\longrightarrow 2NO_2(g)$ has positive entropy change.