For which of the following processes will DeltaΔS be negative? PbCl2 (s) = Pb2 + (aq) + 2 Cl - (aq) MgO (s) + CO2 (g) = MgCO3 (s) CO2 (aq) = CO2 (g) C5H12 (l) + 8 O2 (g) = 5 CO2 (g) + 6 H2O (g)

MgO (s) + CO2 (g) = MgCO3 (s)

Explanation:

Entropy ΔS, simply refers to degree of disorderliness in a system.

In a solid, the particles are locked in place and highly ordered, the clear opposite of disorder or entropy. The atoms can hardly move around in a solid's rigid structure and so their opportunities for spreading out are minimal.

The entropy of the liquid phase is higher. The particles are no longer locked in place. Because they are now free to move, they can distribute themselves in more ways. Like a solid, the molecules can vibrate; but because they have more freedom of movement, molecules have rotational and some translational energy, too.

Gases have the highest entropy values because they have the greatest freedom of movement. Gas particles are separate and distribute themselves throughout their container. And, gases also possess all three types of energy: translational, rotational, and vibrational.

Finally, a substance that is dissolved in a liquid also has a high level of entropy for reasons similar to gases. Dissolved particles are free to not only move throughout the volume of the liquid, but also to move in all three ways. Generally speaking, the entropy value of a dissolved substance is higher than pure liquids but less than gases. To summarize, the entropy of the phases of matter are:

Solid < Liquid < Dissolved < Gas

Observing the phase change among the options, we see that option B satisfies the requirements for a negative ΔS.