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Questions and Answers
Which statement accurately describes the relationship between alkane structure and London Dispersion Forces (LDFs)?
Which statement accurately describes the relationship between alkane structure and London Dispersion Forces (LDFs)?
- Straight-chain alkanes exhibit higher LDFs due to increased surface area for intermolecular interactions. (correct)
- LDFs are independent of the alkane's structure and depend only on the molar mass.
- Branched alkanes exhibit higher LDFs due to increased molecular entanglement.
- Cyclic alkanes exhibit lower LDFs when compared to straight chain alkanes.
How does increasing chain length affect the viscosity and density of alkanes?
How does increasing chain length affect the viscosity and density of alkanes?
- Both viscosity and density decrease due to reduced intermolecular forces.
- Viscosity decreases, and density increases because of branching.
- Viscosity increases, and density decreases due to increased molecular entanglement.
- Both viscosity and density increase due to the increased strength of London dispersion forces. (correct)
Which of the following factors contributes most to the solubility characteristics of alkanes in various solvents?
Which of the following factors contributes most to the solubility characteristics of alkanes in various solvents?
- The ability of alkanes to form hydrogen bonds with water molecules.
- The high reactivity of alkanes with both polar and nonpolar solvents.
- The polar nature of alkanes, allowing them to dissolve in polar solvents.
- The nonpolar nature of alkanes, which promotes solubility in organic solvents with similar polarity. (correct)
Which statement best describes the flammability trend among alkanes as their chain length increases?
Which statement best describes the flammability trend among alkanes as their chain length increases?
How does branching in alkanes affect their boiling points, and why?
How does branching in alkanes affect their boiling points, and why?
Compared to water, what is a general property of alkane density?
Compared to water, what is a general property of alkane density?
How does the physical state of an alkane change as the number of carbon atoms increases, and why?
How does the physical state of an alkane change as the number of carbon atoms increases, and why?
Which property of alkanes is primarily responsible for their use as fuels?
Which property of alkanes is primarily responsible for their use as fuels?
Flashcards
Alkanes
Alkanes
Hydrocarbons with only single bonds between carbon atoms.
Saturated hydrocarbons
Saturated hydrocarbons
Alkanes are saturated, meaning they contain the maximum number of hydrogen atoms possible for a given number of carbon atoms.
Physical states of alkanes
Physical states of alkanes
The physical state of an alkane depends on its chain length.
Boiling point of alkanes
Boiling point of alkanes
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Branching effect on boiling point
Branching effect on boiling point
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Solubility of alkanes
Solubility of alkanes
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Flammability of alkanes
Flammability of alkanes
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Volatility
Volatility
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Study Notes
General Properties
- Alkanes are a class of hydrocarbons characterized by single covalent bonds between carbon and hydrogen atoms.
- They are saturated hydrocarbons, meaning they contain the maximum possible number of hydrogen atoms for a given number of carbon atoms.
- Alkanes are generally nonpolar molecules due to the similar electronegativities of carbon and hydrogen.
- They are relatively unreactive because of the strong C-C and C-H bonds.
Physical States
- The physical states of alkanes depend on the number of carbon atoms in the molecule.
- Shorter chain alkanes (1-4 carbons) are gases at room temperature.
- Alkanes with 5-17 carbons are typically liquids at room temperature.
- Alkanes with 18 or more carbons are solids at room temperature.
Boiling Points
- Boiling points generally increase with increasing molecular weight (more carbons) due to stronger London Dispersion Forces (LDFs).
- More surface area available for intermolecular attractions results in a higher boiling point.
- Branching of the alkyl chain reduces the surface area for intermolecular interactions in comparison to straight-chain alkanes of the similar molar mass. Consequently, branching leads to lower boiling points.
Melting Points
- Melting points also increase with increasing molecular weight and branching effect also influences melting points in a similar manner as boiling points.
Solubility
- Alkanes are essentially insoluble in water due to their nonpolar nature and the strong hydrogen bonds formed in water molecules.
- Alkanes are however soluble in organic solvents, especially those with similar polarity.
Density
- Alkanes are generally less dense than water.
- Density increases slightly with increasing molecular weight.
Viscosity
- Viscosity increases with increasing molecular weight due to the increased strength of London dispersion forces.
- Branching of the chain also affects viscosity. A branched alkane will have a lower viscosity than a straight chain alkane of equal molar mass.
Flammability
- Alkanes are highly flammable, meaning they readily react with oxygen to form carbon dioxide and water.
- The reaction is exothermic, releasing a significant amount of energy as heat.
- The flammability of alkanes decreases slightly with increasing chain length and branching.
Volatility
- Volatility refers to the tendency of a liquid to vaporize.
- Alkanes with lower molecular weights are more volatile due to weaker intermolecular forces.
- Branching of the chain decreases volatility.
Optical Properties
- Alkanes are generally transparent and colorless.
- They exhibit no noticeable color change in the visible region of the electromagnetic spectrum.
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