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Alkanes Knowledge-Based Practice

Chemistry · Organic Chemistry · Chemistry · Hydrocarbons

5 Chemistry practice questions on Alkanes. Questions that assess core concepts and understanding.

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Questions

  1. 1.

    Which statement correctly compares the staggered and eclipsed conformations of ethane?

    • A) The eclipsed conformation has a lower potential energy due to stabilizing interactions between overlapping C–H bonds.
    • B) The staggered conformation has a dihedral angle of 0° between adjacent C–H bonds, which maximizes torsional strain.
    • C) The eclipsed conformation is more thermodynamically stable because electron-electron repulsion between adjacent bonds is minimized.
    • D) The staggered conformation has a lower potential energy because torsional strain is minimized when adjacent C–H bonds are maximally separated.
  2. 2.

    During the photochemical chlorination of methane, which of the following reactions represents a chain propagation step?

    • A) Cl2→hν2 Cl∙\text{Cl}_2 \xrightarrow{h\nu} 2\,\text{Cl}^\bullet
    • B) 2 Cl∙→Cl22\,\text{Cl}^\bullet \rightarrow \text{Cl}_2
    • C) CH3∙+Cl∙→CH3Cl\text{CH}_3^\bullet + \text{Cl}^\bullet \rightarrow \text{CH}_3\text{Cl}
    • D) CH4+Cl∙→CH3∙+HCl\text{CH}_4 + \text{Cl}^\bullet \rightarrow \text{CH}_3^\bullet + \text{HCl}
  3. 3.

    Which of the following statements best explains why a branched alkane has a lower boiling point than its straight-chain constitutional isomer with the same molecular formula?

    • A) Branched alkanes have lower boiling points because their permanent dipole moments cancel out completely in the liquid state.
    • B) Branched alkanes possess a larger effective surface area that prevents adjacent molecules from forming stable aggregates.
    • C) Branched alkanes adopt a more spherical shape, reducing surface contact and weakening intermolecular London dispersion forces.
    • D) Branched alkanes require less thermal energy to boil because their intramolecular carbon-carbon covalent bonds break more readily.
  4. 4.

    What is the IUPAC name for the alkane represented by the condensed formula CH3CH(CH3)CH2CH(CH2CH3)CH2CH3\text{CH}_3\text{CH}(\text{CH}_3)\text{CH}_2\text{CH}(\text{CH}_2\text{CH}_3)\text{CH}_2\text{CH}_3?

    • A) 2-Methyl-4-ethylhexane
    • B) 3-Ethyl-5-methylhexane
    • C) 4-Ethyl-2-methylhexane
    • D) 2,4-Dimethylheptane
  5. 5.

    How many constitutional isomers exist for an open-chain alkane having the molecular formula C5H12C_5H_{12}?

    • A) 3
    • B) 4
    • C) 5
    • D) 2

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