The standard heat of formation values of SF6(g), S(g) and F(g) are: −1100, 275 and 80 kJ mol−1 respectively. Then the average S − F bond energy in SF6.
Correct answer: C. 309 kJ mol−1
- A. 301 kJ mol−1
- B. 320 kJ mol−1
- C. 309 kJ mol−1
- D. 280 kJ mol−1
Explanation
To find the average S-F bond energy in SF6, we need to use the concept of bond energies and the given standard heat of formation values. The average S-F bond energy in SF6 can be calculated using the following equation: Average S-F bond energy= [ΔHf(SF6) - ΔHf(S) - 6 x ΔHf(F)] /6 where ΔHf represents the standard heat of formation. Given values: ΔHf(SF6) = -1100 kJ mol-1 ΔHf(S) = 275 kJ mol-1 ΔHf(F) = 80 kJ mol-1 Let's plug in the values: Average S-F bond energy = [-1100 - 275 - 6 x 80] / 6 Average S-F bond energy = [-1100 - 275 - 480] / 6 Average S-F bond energy = -1855/6 ≈ -309 kJ mol-1
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About Bond Energy
Bond energy is the energy needed to break one mole of a particular covalent bond in gaseous molecules, while bond formation releases energy. Reaction enthalpy is estimated by subtracting the total energy of bonds formed from bonds broken, with attention to average bond energies and their limitations for specific molecules.
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