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Bond enthalpies

Chemistry • Enthalpy • Knowledge-Based • 5 questions

Bond enthalpies Knowledge-Based Download PDF

Chemistry · Thermochemistry & Thermodynamics · Chemistry · Enthalpy

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

Questions

  1. 1.

    Which chemical equation represents the process defining the bond dissociation enthalpy of hydrogen bromide?

    • A) HBr(g)→H(g)+Br(g)\text{HBr(g)} \rightarrow \text{H(g)} + \text{Br(g)}
    • B) HBr(g)→12H2(g)+12Br2(l)\text{HBr(g)} \rightarrow \frac{1}{2}\text{H}_2\text{(g)} + \frac{1}{2}\text{Br}_2\text{(l)}
    • C) HBr(g)→H+(g)+Br−(g)\text{HBr(g)} \rightarrow \text{H}^+\text{(g)} + \text{Br}^-\text{(g)}
    • D) HBr(aq)→H+(aq)+Br−(aq)\text{HBr(aq)} \rightarrow \text{H}^+\text{(aq)} + \text{Br}^-\text{(aq)}
  2. 2.

    Which statement correctly describes the general relationship between bond order, bond length, and bond enthalpy across carbon–carbon single, double, and triple bonds?

    • A) As bond order increases, bond length increases and bond enthalpy increases.
    • B) As bond order increases, bond length decreases and bond enthalpy increases.
    • C) As bond order increases, bond length decreases and bond enthalpy decreases.
    • D) As bond order increases, bond length increases and bond enthalpy decreases.
  3. 3.

    Given the average bond enthalpies of C−H\text{C}-\text{H} (414 kJ/mol), Cl−Cl\text{Cl}-\text{Cl} (242 kJ/mol), C−Cl\text{C}-\text{Cl} (339 kJ/mol), and H−Cl\text{H}-\text{Cl} (431 kJ/mol), what is the estimated enthalpy change (ΔH\Delta H) for the reaction CH4(g)+Cl2(g)→CH3Cl(g)+HCl(g)\text{CH}_4\text{(g)} + \text{Cl}_2\text{(g)} \rightarrow \text{CH}_3\text{Cl(g)} + \text{HCl(g)}?

    • A) +114 kJ/mol
    • B) -97 kJ/mol
    • C) -114 kJ/mol
    • D) +228 kJ/mol
  4. 4.

    For the gas-phase reaction N2(g)+3H2(g)→2NH3(g)\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightarrow 2\text{NH}_3\text{(g)}, the reaction enthalpy is ΔH=−93 kJ/mol\Delta H = -93\text{ kJ/mol}. Given that the average bond enthalpy of H−H\text{H}-\text{H} is 436 kJ/mol and that of N−H\text{N}-\text{H} is 391 kJ/mol, what is the bond enthalpy of the N≡N\text{N}\equiv\text{N} triple bond?

    • A) 852 kJ/mol
    • B) 1131 kJ/mol
    • C) 945 kJ/mol
    • D) 759 kJ/mol
  5. 5.

    Given the average bond enthalpies for C=C\text{C}=\text{C} (614 kJ/mol), C−C\text{C}-\text{C} (348 kJ/mol), H−H\text{H}-\text{H} (436 kJ/mol), and C−H\text{C}-\text{H} (413 kJ/mol), what is the enthalpy change of the reaction C2H4(g)+H2(g)→C2H6(g)\text{C}_2\text{H}_4\text{(g)} + \text{H}_2\text{(g)} \rightarrow \text{C}_2\text{H}_6\text{(g)}?

    • A) +124 kJ/mol
    • B) -826 kJ/mol
    • C) -124 kJ/mol
    • D) +248 kJ/mol