Predict the sign of ΔSsys for each of the following processes: (a) Molten gold solidifies. (b)

Predict the sign of ΔSsys for each of the following...

Predict the sign of $\Delta S_{\text {sys }}$ for each of the following processes: (a) Molten gold solidifies. (b) Gaseous $\mathrm{Cl}_{2}$ dissociates in the stratosphere to form gaseous $\mathrm{Cl}$ atoms. (c) Gaseous CO reacts with gaseous $\mathrm{H}_{2}$ to form liquid methanol, $\mathrm{CH}_{3} \mathrm{OH}$. (d) Calcium phosphate precipitates upon mixing $\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}(a q)$ and $\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}(a q)$

Predict the sign of $\Delta S_{\text {sys }}$ for each of the following processes:
(a) Molten gold solidifies. (b) Gaseous $\mathrm{Cl}_{2}$ dissociates in the stratosphere to form gaseous $\mathrm{Cl}$ atoms. (c) Gaseous CO reacts with gaseous $\mathrm{H}_{2}$ to form liquid methanol, $\mathrm{CH}_{3} \mathrm{OH}$.
(d) Calcium phosphate precipitates upon mixing $\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}(a q)$ and $\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}(a q)$

Key Concepts

Precipitation Reactions

Precipitation reactions involve the formation of a solid, often from ions in solution. This process decreases the entropy of the system because the ions become part of a well-ordered crystal lattice, reducing the overall randomness and the number of microstates available compared to when they were dispersed in solution.

Molecular Dissociation and Association

Reactions that involve the breaking apart (dissociation) of molecules typically increase entropy by producing a larger number of particles, thereby increasing the number of microstates. Conversely, reactions that involve the combination (association) of molecules tend to decrease entropy as they reduce the number of freely moving particles.

Thermodynamic Entropy

Entropy is a central concept in thermodynamics that measures the degree of disorder or randomness within a system. It quantifies the number of microscopic configurations that correspond to the macroscopic state, and processes that increase disorder result in a positive change in entropy, while those that increase order lead to a negative change.

Phase Transitions

Phase transitions, such as melting, solidification, evaporation, and condensation, greatly affect entropy. Generally, gases have higher entropy compared to liquids, and liquids have higher entropy than solids because the particles in the gas phase have more freedom of movement and a larger number of accessible microstates.

Transcript

00:01 Let's take a look at whether the change in entropy of our system goes up or down during these various processes.

00:08 In the first part, we have liquid gold solidifying, so turning into solid gold.

00:16 And as we go from a liquid to a solid where intermolecular forces are created, the molecules are, if you will, stuck together.

00:26 And as those atoms are stuck together, we have less freedom of motion.

00:33 And if we have less freedom, we have fewer configurations or microstates that gold can be in as a solid, which results in lowering the entropy.

00:50 In the second part, we have gaseous cl2, forming two gaseous cl atoms.

01:00 So we're breaking one mole of a substance into two moles of a substance, both gases.

01:06 And so since we're going from one mole of gas to two moles of gas, we're increasing the freedom of the particles.

01:16 They have more potential configurations they can be in, more microscure.

01:19 States the entropy goes up.

01:24 In the third example, we have two gases, carbon monoxide and hydrogen forming methanol.

01:33 The two reactants are gases and the product is a liquid.

01:37 So we're reducing the freedom going from a gas to a liquid.

01:41 We're also overall reducing the number of moles in this process.

01:45 More important is the gas going to a liquid.

01:48 When we form those intermolecular forces and we create fewer molecules.

01:55 In both cases, we're reducing the freedom.

02:00 And when we reduce the freedom, we reduce the number of microstates that can't move around as much and as randomly as it once did.

02:10 That is going to reduce entropy.

02:15 And finally, we're doing a precipitation or a double replacement reaction between calcium nitrate and ammonium phosphate to create calcium phosphate and ammonium nitrate.

02:26 So here's the balanced equation...

Please give Ace some feedback