Question

Of the following reactions occurring at 25ºC, which one involves the greatest increase in entropy?H2(g) + Cl2(g) = 2 HCl(g)H2O(s) = H2O(l)Pb2+(aq) + 2 Cl-(aq) = PbCl2(s)CO2(s) = CO2(g)

Answer 1

Answer: [tex]CO_2(s)\rightarrow CO_2(g)[/tex]

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) $H_2(g)+Cl_2(g)\rightarrow 2HCl(g)$

2 molesof gas are converting to 2 moles of another gas , thus $\Delta S$ is zero.

b) $H_2O(s)\rightarrow H_2O(l)$

1 mole of solid is converting to 1 mole of liquid, the randomness increases and thus $\Delta S$ is positive.

b) $Pb^{2+}(aq)+2Cl^-(aq)\rightarrow PbCl_2(s)$

2 moles of ions are converting to 1 mole of solid, the randomness decreases and thus $\Delta S$ is negative

d) $CO_2(s)\rightarrow CO_2(g)$

1 mole of solid is converting to 1 mole of gas, the randomness increases drastically and thus $\Delta S$ is highly positive.