High School

Calculate the average C−F bond energy from the following data:

The heat of atomization of CH₄ is 1660 kJ/mol and of CH₂F₂ is 1798 kJ/mol.

a) 69 kJ/mol
b) 72 kJ/mol
c) 75 kJ/mol
d) 78 kJ/mol

Answer :

Final Answer:

69 kJ/mol is the average C−F bond energy, thus the correct answer is: a) 69 kJ/mol

Explanation:

The average C₋F bond energy can be calculated using the heat of atomization data for CH₄ and CH₂F₂. The difference in the heats of atomization provides the energy required to break the C₋H bonds in CH₄ and replace them with C₋F bonds in CH₂F₂.

Firstly, find the energy change for breaking C₋H bonds in CH₄:

ΔH(CH₄) = Heat of atomization of CH₄

ΔH(CH₄) = 1660 kJ/mol

Then, find the energy change for breaking C₋H bonds and forming C₋F bonds in CH₂F₂:

ΔH(CH₂F₂) = Heat of atomization of CH₂F₂

ΔH(CH₂F₂) = 1798 kJ/mol

Now, subtract the energy change for CH₄ from that of CH₂F₂ to get the energy change for replacing C₋H with C₋F bonds:

ΔH(C₋F) = ΔH(CH₂F₂) - ΔH(CH₄)

ΔH(C₋F) = 1798 kJ/mol - 1660 kJ/mol

ΔH(C₋F) = 138 kJ/mol

Since there are two C₋F bonds formed in the process, calculate the average C₋F bond energy:

Average C₋F bond energy = ΔH(C₋F) / Number of bonds

Average C₋F bond energy = 138 kJ/mol / 2

Average C₋F bond energy = 69 kJ/mol

Considering the given options, the closest answer is: a) 69 kJ/mol

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