The reasons for butane to exist as gas and hexane as liquid at room temperature are to be determined. Concept Introduction: A hydrocarbon is organic compound consisting entirely of hydrogen and carbon. Butane and hexane both are hydrocarbon. Butane is a four-carbon alkane and hexane contains six carbon atoms. The temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere is called boiling point. Boiling point of a molecule depends on the intermolecular forces and thermal energy. Intermolecular forces are of two types: dispersion forces and dipole forces. Dispersion forces are possessed by all the atoms or molecules, which depend on the molar mass. Dipole forces exist between polar molecules, which depend on the polarity of the molecules. Intermolecular forces keep the molecules together. Greater the intermolecular force, higher is the boiling point. All atoms and molecules possess dispersion forces which depend upon their molar mass. Polar molecules possess dipole forces between them which depend upon the polarity of the molecules. A molecular formula consists of the chemical symbols for the constituent elements followed by numeric subscripts describing the number of atoms of each element present in the molecule. Dispersion forces are weak intermolecular forces and are considered van der waals forces. Temporary dipoles can occur in non-polar molecules when the electrons that constantly orbit the nucleus occupy a similar location by chance. Higher the molar mass, higher is the magnitude of the dispersion forces, and hence, higher is the boiling point. Molecules which have lower molar masses have lower dispersion forces because dispersion force is directly proportional to the molar mass. Molecules which have higher molar masses have higher dispersion forces.

Question

Propane boils at -42 degree Celsius, ethanal boils at 20.8 degree Celsius and ethanol boils at 78.3 degree Celsius. Although their molecular masses are very similar, their boiling points are very different, explain why?

Answer 1

Question

Chapter 12, Problem 27E

Interpretation Introduction

Interpretation:

The reasons for butane to exist as gas and hexane as liquid at room temperature are to be determined.

Concept Introduction:

A hydrocarbon is organic compound consisting entirely of hydrogen and carbon.

Butane and hexane both are hydrocarbon. Butane is a four-carbon alkane and hexane contains six carbon atoms.

The temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere is called boiling point.

Boiling point of a molecule depends on the intermolecular forces and thermal energy.

Intermolecular forces are of two types: dispersion forces and dipole forces.

Dispersion forces are possessed by all the atoms or molecules, which depend on the molar mass.

Dipole forces exist between polar molecules, which depend on the polarity of the molecules.

Intermolecular forces keep the molecules together. Greater the intermolecular force, higher is the boiling point.

All atoms and molecules possess dispersion forces which depend upon their molar mass.

Polar molecules possess dipole forces between them which depend upon the polarity of the molecules.

A molecular formula consists of the chemical symbols for the constituent elements followed by numeric subscripts describing the number of atoms of each element present in the molecule.

Dispersion forces are weak intermolecular forces and are considered van der waals forces.

Temporary dipoles can occur in non-polar molecules when the electrons that constantly orbit the nucleus occupy a similar location by chance.

Higher the molar mass, higher is the magnitude of the dispersion forces, and hence, higher is the boiling point.

Molecules which have lower molar masses have lower dispersion forces because dispersion force is directly proportional to the molar mass.

Molecules which have higher molar masses have higher dispersion forces.

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