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Ch.18 - Free Energy and Thermodynamics
Tro - Chemistry: A Molecular Approach 4th Edition
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Tutti i libri di testoTro 4th EditionCh.18 - Free Energy and ThermodynamicsProblema 36
Capitolo 18, Problema 36

Without doing any calculations, determine the sign of ΔSsys for each chemical reaction. a. Mg(s) + Cl2(g) → MgCl2(s) b. 2 H2S(g) + 3 O2(g) → 2 H2O(g) + 2 SO2(g) c. 2 O3(g) → 3 O2(g) d. HCl(g) + NH3(g) → NH4Cl(s)

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Identify the states of matter for each reactant and product in the reactions.
Recall that entropy (ΔS) is a measure of disorder or randomness in a system, with gases having higher entropy than liquids or solids.
For reaction (a), note that a gas and a solid react to form a solid, indicating a decrease in entropy (ΔSsys < 0).
For reaction (b), compare the number of gas molecules on both sides of the equation. The number of gas molecules remains the same, suggesting a small change in entropy (ΔSsys ≈ 0).
For reaction (c), observe that the reaction goes from 2 moles of gas to 3 moles of gas, indicating an increase in entropy (ΔSsys > 0).

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Entropy (ΔS)

Entropy, denoted as ΔS, is a measure of the disorder or randomness in a system. In chemical reactions, changes in entropy can indicate whether the products are more or less disordered than the reactants. A positive ΔS suggests an increase in disorder, while a negative ΔS indicates a decrease in disorder.
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Entropy in Thermodynamics

Phase Changes and Entropy

The phase of a substance significantly affects its entropy. Gases have higher entropy than liquids, which in turn have higher entropy than solids due to the greater freedom of movement and arrangement of particles in gases. Therefore, reactions that produce gases from solids or liquids typically result in a positive ΔS.
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Entropy in Phase Changes

Molecular Complexity and Entropy

The complexity and number of molecules in a reaction can influence entropy. Reactions that produce more molecules or more complex molecules generally lead to an increase in entropy. Conversely, reactions that result in fewer or simpler molecules tend to decrease the system's entropy.
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Factors Affecting Entropy
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Without doing any calculations, determine the sign of ΔSsys for each chemical reaction. b. CH2=CH2( g) + H2( g) → CH3CH3( g)

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