Question

Which of the following processes have a ?S > 0?

2HCl(g) ? H2(g) + Cl2(l)
2NH3(g) + CO2(g) ? NH2CONH2(aq) + H2O(l)
lithium fluoride forms from its elements
cesium chloride dissolves in pure water
All of the above processes have a ?S > 0

Answer 1

Answer: Cesium chloride dissolves in pure water has $\Delta S$ > 0.

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

As 2 moles of gas are converting to 1 mole of gas and 1 mole of liquid, the randomness decreases and hence $\Delta S$ is negative.

b) $2NH_3(g)+CO_2(g)\rightarrow NH_2CONH_2(aq)+H_2O(l)$

As gas molecules are converting into aqueous and liquid form,  the randomness decreases and hence $\Delta S$ is negative.

c) lithium fluoride forms from its elements: $2Li+F_2\rightarrow 2LiF$

As elements are combining to form a compound, the randomness decreases and hence $\Delta S$ is negative.

d) Cesium chloride dissolves in pure water : $CaCl_2(s)\rightarrow Ca^{2+}(aq)+2Cl^-(aq)$

As compound is dissociating into ions, the randomness increases and hence $\Delta S$ is positive.