(a) What do you expect for the sign of ΔS in a chemical reaction in which two moles of gaseous r

(a) What do you expect for the sign of ΔS in a chemical...

(a) What do you expect for the sign of $\Delta S$ in a chemical reaction in which two moles of gaseous reactants are converted to three moles of gaseous products? (b) For which of the processes in Exercise 19.11 does the entropy of the system increase?

Key Concepts

Phase and Molecular Number Changes

Processes that involve changes in the phase of substances or the number of particles, such as the conversion of fewer moles of gas to more moles of gas, typically lead to an increase in the system’s entropy. This reflects the broader principle that systems evolve toward states with greater dispersal of energy and matter.

Reaction Stoichiometry

The stoichiometry of a chemical reaction, especially in terms of the number of moles of gaseous reactants and products, plays a critical role in determining the change in entropy. Reactions that increase the total number of gas molecules tend to increase entropy because there are more ways to distribute energy among the particles.

Entropy

Entropy is a thermodynamic property that quantifies the level of disorder or randomness in a system. In the context of chemical reactions, it is used to measure how the distribution of energy among the particles changes, with a greater number of accessible microstates being associated with higher entropy.

Transcript

00:02 Let's see what happens to the entropy of a number of different systems when we act upon a process.

00:12 So in the first example, we have three moles of a gas, and we're going to reduce that to two moles of a gas.

00:21 And remember that entropy is affected by the number of particles that a system has, the more particles there are, the higher than.

00:32 Entropy and the state of matter that it's in.

00:36 As we break intermolecular forces going from a solid to a liquid to a gas, we create more particles, which creates more disorder and more entropy.

00:46 So when we reduce the number of moles of gas, we're actually creating a more ordered system, and the entropy of that system is going to go down.

00:56 We have fewer possible states, possible configurations that these molecules can be in.

01:04 In the next example, we have a banana ripening.

01:09 And in and of itself, it's staying the same state of matter for the most part.

01:14 You might be able to make an argument that as it ripens and starts to decompose, you get some more gases, you start smelling that.

01:24 And so in this case, we could say that as that solid goes ahead and start softening and become more liquidy or letting some gases out, that we're creating more possible states that these molecules can be in, increasing the entropy.

01:46 When we dissolve sugar, we're taking that solid and we are interacting it with water or other substances such that the intermolecular forces get rearranged, normally making an aqueous system, and once that solid winds up being aqueous, it interacts with water as a separated substance.

02:15 We've created more possible states configurations that these particles can be in.

02:22 That is going to increase the entropy...

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