Chapter 2.7: Physical Properties of Alkanes and Cycloalkanes

Question 1

What are very weak intermolecular forces of attraction resulting from the interaction between temporary induced dipoles?

Answer 1

dispersion forces

Question 2

Define dispersion forces

Answer 2

very weak intermolecular forces of attraction resulting from the interaction between temporary induced dipoles

Question 3

How does boiling point decrease with increased branching in alkanes?

Answer 3

Branching increase –> shape becomes more compact –> surface area decreases –> contact among adjacent molecules decreases –> dispersion forces increase –> boiling point decreases

Question 4

Describe the relationship between boiling/melting point and molecular weight

Answer 4

o Boiling point and melting point increase as molecular weight increases

Question 5

What is the most important property of alkanes and cycloalkanes?

Answer 5

• The most important property of alkanes and cycloalkanes is their almost complete lack of polarity

Question 6

Describe the relationship between dispersion forces and molar mass

Answer 6

o Strength of dispersion forces tends to increase with increasing molar mass

Question 7

Describe the relationship between branched alkanes and boiling point

Answer 7

o For any group of alkane constitutional isomers, the least branched isomer usually has the highest boiling point and the most branched isomer usually has the lowest boiling point

Question 8

Relate liquid and solid alkanes to water in terms of density

Answer 8

o All liquid and solid alkanes are less dense than water