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.

Step-by-step 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.