Using data in Appendix 11 , determine ΔS^∘(298 K) for the following reactions: (a) 2 Fe(s)+3 Cl2

step 1 In this question, we will be covering the topic of Gibbs free energy and learning how to calcula

Using data in Appendix 11 , determine ΔS^∘(298 K) for the...

Using data in Appendix 11 , determine $\Delta S^{\circ}(298 \mathrm{K})$ for the following reactions: (a) $2 \mathrm{Fe}(\mathrm{s})+3 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{FeCl}_{3}(\mathrm{s})$ (b) $\mathrm{Fe}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{g}) \rightarrow \mathrm{FeCl}_{2}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{g})$ (c) $\mathrm{CaCO}_{3}(\mathrm{s})-\mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g})$ Which reactions are entropically favoured?

Using data in Appendix 11 , determine $\Delta S^{\circ}(298 \mathrm{K})$ for the following reactions:
(a) $2 \mathrm{Fe}(\mathrm{s})+3 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{FeCl}_{3}(\mathrm{s})$
(b) $\mathrm{Fe}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{g}) \rightarrow \mathrm{FeCl}_{2}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{g})$
(c) $\mathrm{CaCO}_{3}(\mathrm{s})-\mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g})$
Which reactions are entropically favoured?

Key Concepts

Entropy Favoured Reactions

An entropically favoured reaction is one that has a positive standard entropy change (?S° > 0), indicating that the disorder of the system increases as the reaction proceeds. Such reactions are more likely to occur spontaneously at higher temperatures, as the increase in entropy may overcome enthalpic drawbacks according to the Gibbs free energy relationship.

Calculation of Reaction Entropy Change

This involves applying the equation ?S° = ?S°(products) - ?S°(reactants). The calculation requires careful consideration of stoichiometry, as each substance's standard molar entropy must be multiplied by its coefficient in the balanced chemical equation. This method is used to predict whether a reaction will lead to an increase or decrease in the overall disorder.

Phase Effects on Entropy

The phase of a substance has a significant impact on its entropy. Gases typically have much higher entropy than liquids, which in turn have higher entropy than solids, due to the greater freedom of movement and higher number of accessible microstates. When analyzing reactions, the formation or consumption of gaseous reactants or products plays a key role in determining the overall entropy change.

Standard Entropy Change (?S°)

This concept refers to the change in entropy under standard conditions (usually 298 K and 1 atm) when reactants are converted to products. It is determined by subtracting the sum of the standard molar entropies of the reactants from that of the products. A positive ?S° indicates an increase in disorder, while a negative value suggests a decrease.

Standard Molar Entropies

Standard molar entropy values quantify the absolute disorder of substances in their standard states. They are typically tabulated in thermodynamic data sets and are essential for calculating the overall entropy change of a reaction. These values depend on the phase and molecular structure of the substances, with gases usually having the highest entropies, followed by liquids and then solids.

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