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Question
Chemistry
Posted 7 months ago

\begin{tabular}{|c|c|}
\hline \multicolumn{2}{|c|}{ [Substane| S(J mol KS^{\circ}\left(\frac{J}{\mathrm{~mol}^{*} \mathrm{~K}}\right.} \\
\hline C(s graphite) & 5.7 \\
\hline C(s diamond & d) 2.4 \\
\hline H(g)\mathrm{H}(\mathrm{g}) & 114.7 \\
\hline H2( g)\mathrm{H} 2(\mathrm{~g}) & 130.7 \\
\hline Cl(g)\mathrm{Cl}(\mathrm{g}) & 165.2 \\
\hline Cl2( g)\mathrm{Cl} 2(\mathrm{~g}) & 223.1 \\
\hline C3Cl(g)\mathrm{C} 3 \mathrm{Cl}(\mathrm{g}) & 234.6 \\
\hline
\end{tabular}

Part A
Find the deltaSdegree for the formation of CH3Cl(g)\mathrm{CH3Cl}(\mathrm{g}) from its elements in their standard states
deltaSrxn =J/K=J / K
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Answer from Sia
Posted 7 months ago
Solution
1
Write the balanced chemical equation for the formation of CH3Cl(g): The formation of CH3Cl(g) from its elements in their standard states can be represented by the following equation: C(s,graphite)+3H2(g)+12Cl2(g)CH3Cl(g)C_{(s, graphite)} + 3H_2(g) + \frac{1}{2}Cl_2(g) \rightarrow CH_3Cl(g)
2
Calculate the change in standard entropy (ΔS°): The change in standard entropy for the reaction (ΔS°rxn) is calculated using the standard molar entropies (S°) of the reactants and products. The formula to calculate ΔS°rxn is: ΔSrxn=SproductsSreactants\Delta S^\circ_{rxn} = S^\circ_{products} - S^\circ_{reactants}. Using the values from the table: ΔSrxn=SCH3Cl(g)(SC(s,graphite)+3SH2(g)+12SCl2(g))\Delta S^\circ_{rxn} = S^\circ_{CH3Cl(g)} - \left( S^\circ_{C(s, graphite)} + 3S^\circ_{H_2(g)} + \frac{1}{2}S^\circ_{Cl_2(g)} \right). Plugging in the values: ΔSrxn=234.6 J/(molK)(5.7 J/(molK)+3×130.7 J/(molK)+12×223.1 J/(molK))\Delta S^\circ_{rxn} = 234.6\ J/(mol\cdot K) - \left( 5.7\ J/(mol\cdot K) + 3 \times 130.7\ J/(mol\cdot K) + \frac{1}{2} \times 223.1\ J/(mol\cdot K) \right)
3
Perform the calculation: Now we perform the arithmetic: ΔSrxn=234.6(5.7+392.1+111.55)=234.6509.35=274.75 J/(molK)\Delta S^\circ_{rxn} = 234.6 - (5.7 + 392.1 + 111.55) = 234.6 - 509.35 = -274.75\ J/(mol\cdot K)
Answer
-274.8 J/(mol*K)
Key Concept
Entropy change for a reaction
Explanation
The entropy change for a reaction is calculated by subtracting the sum of the standard molar entropies of the reactants from the sum of the standard molar entropies of the products.

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