A chemist records the following data for two hypothetical substances: • Substance X:…

CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics

Problem

A chemist records the following data for two hypothetical substances: • Substance X:

\Delta H_{\text{fus}} = 5.5\,\text{kJ\,mol}^{-1}

\Delta H_{\text{vap}} = 25.0\,\text{kJ\,mol}^{-1}

M = 50.0\,\text{g\,mol}^{-1}

• Substance Y:

\Delta H_{\text{fus}} = 7.0\,\text{kJ\,mol}^{-1}

\Delta H_{\text{vap}} = 20.0\,\text{kJ\,mol}^{-1}

M = 40.0\,\text{g\,mol}^{-1}

Consider the following processes at

1\,\text{atm}

: I. Melting

120\,\text{g}

of X at its melting point II. Vaporizing

60\,\text{g}

of Y at its boiling point III. Vaporizing

120\,\text{g}

of X at its boiling point Which ranking correctly orders the processes from greatest to least heat absorbed? (a) II > III > I (b) I > III > II (c) III > II > I (d) III > I > II

Related theory

Thermodynamics

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