Chemistry

Problem

Graphite burns in pure oxygen according to the equation

C(\text{graphite}) + O_2(g) \to CO_2(g)

For this reaction at

298\,\text{K}

the standard entropy change is

\Delta S^\circ_{\text{rxn}} = -179.0\,\text{J mol}^{-1}\,\text{K}^{-1}

. Additional information is provided in mixed units. Substance S°

C(\text{graphite})

0.34\,\text{cal mol}^{-1}\,\text{K}^{-1}

CO_2(g)

213.6\,\text{J mol}^{-1}\,\text{K}^{-1}

The accepted literature value for the standard molar entropy of

O_2(g)

298\,\text{K}

205.0\,\text{J mol}^{-1}\,\text{K}^{-1}

. (a) Convert the standard molar entropy of

C(\text{graphite})

to SI units with the correct number of significant figures. (b) Using the data above, determine the standard molar entropy of

O_2(g)

298\,\text{K}

. (c) Calculate the percent error of your result in part (b) relative to the literature value and comment on one plausible experimental or tabulation source of this discrepancy.

Intuitive explanation

This problem tests your understanding of how entropy changes in a reaction relate to the standard molar entropies of individual substances. The key insight is that $\Delta S°_{\text{rxn}}$ equals the sum of products' entropies minus reactants' entropies—but you'll need to carefully convert all values to the same units before plugging them in. Watch out: one entropy value is given in calories, not joules, so unit conversion is essential to getting the right answer.

Intuitive explanation

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