For the reaction CS2(g)+3 O2(g) ⟶CO2(g)+2 SO2(g) ΔS^∘ is equal to -143 J / K. Use this value an

step 1 So for the reaction given, it tells you that the overall entropy, change in entropy, is equal to

For the reaction CS2(g)+3 O2(g) ⟶CO2(g)+2 SO2(g) ΔS^∘ is...

For the reaction
$$\mathrm{CS}_{2}(g)+3 \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{SO}_{2}(g)$$
$\Delta S^{\circ}$ is equal to $-143 \mathrm{~J} / \mathrm{K}$. Use this value and data from Appendix 4 to calculate the value of $S^{\circ}$ for $\mathrm{CS}_{2}(g)$.

Key Concepts

Using Thermodynamic Data for Calculations

Thermodynamic calculations rely on tabulated data such as standard molar entropies to determine unknown values within a chemical reaction. When the overall change in entropy for a reaction is known along with some of the individual substance entropies, the missing entropy value can be calculated by rearranging the entropy balance equation. This method is grounded in the conservation of energy and entropy, drawing on Hess's law-like principles.

Standard Molar Entropy

This is a measure of the randomness or disorder of a substance at a standard state (usually 1 bar pressure and a specified temperature). It represents the amount of energy dispersal at the molecular level and is expressed in units such as joules per mole per Kelvin (J/mol·K). Standard molar entropy values are tabulated for many substances and are used to calculate changes in entropy for chemical reactions.

Reaction Entropy Change

The reaction entropy change (?S°) is the difference between the sum of the standard molar entropies of the products and those of the reactants. It provides insight into the overall change in disorder during a reaction, indicating whether the system becomes more or less randomized as the reaction proceeds. This calculation is essential in predicting the spontaneity of reactions and is performed by applying the equation: ?S° = ?S°(products) - ?S°(reactants).

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