   Chapter 18, Problem 51GQ

Chapter
Section
Textbook Problem

Compare the compounds in each set below and decide which is expected to have the higher entropy. Assume all are at the same temperature. Check your answers using data in Appendix L. (a) HF(g), HCl(g), or HBr(g) (b) NH4Cl(s) or NH4Cl(aq) (c) C2H4(g) or N2(g) (two substances with the same molar mass) (d) NaCl(s) or NaCl(g)

(a)

Interpretation Introduction

Interpretation: From the given set that is HF(g),HCl(g)andHBr(g) the compound with higher entropy should be predicted also that finally the predicted compound has to be checked using data in Appendix L.

Concept introduction: The standard molar entropy is the entropy of a substance which is gained by the conversion of 1 mol of substance from perfect crystal at 0 K to standard conditions. It is represented by the symbol So. Its value depend on various parameters such as temperature, pressure, volume, physical state and molecular structure.

Explanation

Entropy increases in the order solid < liquid < gas. HF, HCl and HBr are in gaseous state. However, the entropy is higher for larger molecules since there are more number of ways to rotate and vibrate the molecules in larger molecule than for smaller molecules. HBr is the largest molecule among the HF, HCl and HBr since Br has increased size than ClandF as size increases from top to bottom down the group. Therefore, the compound with highest entropy is HBr(g)

(b)

Interpretation Introduction

Interpretation: From the given set that is NH4Cl(s)andNH4Cl(aq) the compound with higher entropy should be predicted also that finally the predicted compound has to be checked using data in Appendix L.

Concept introduction: The standard molar entropy is the entropy of a substance which is gained by the conversion of 1 mol of substance from perfect crystal at 0 K to standard conditions. It is represented by the symbol So. Its value depend on various parameters such as temperature, pressure, volume, physical state and molecular structure.

(c)

Interpretation Introduction

Interpretation: From the given set that is C2H4(g)andN2(g) the compound with higher entropy should be predicted also that finally the predicted compound has to be checked using data in Appendix L.

Concept introduction: The standard molar entropy is the entropy of a substance which is gained by the conversion of 1 mol of substance from perfect crystal at 0 K to standard conditions. It is represented by the symbol So. Its value depend on various parameters such as temperature, pressure, volume, physical state and molecular structure.

(d)

Interpretation Introduction

Interpretation: From the given set that is NaCl(s)andNaCl(aq) the compound with higher entropy should be predicted also that finally the predicted compound has to be checked using data in Appendix L.

Concept introduction: The standard molar entropy is the entropy of a substance which is gained by the conversion of 1 mol of substance from perfect crystal at 0 K to standard conditions. It is represented by the symbol So. Its value depend on various parameters such as temperature, pressure, volume, physical state and molecular structure.

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