The strain energy (in kJ/mol) of cyclobutane from the following data:
Δ_f H [C₄H₈(g)] = 28.0 kJ/mol; Δ_f H [C(g)] = 715.0 kJ/mol; Δ_f H [H(g)] = 218.0 kJ/mol
BE (C-C) = 348.0 kJ/mol; BE (C-H) = 412.0 kJ/mol.

Question

The strain energy (in kJ/mol) of cyclobutane from the following data:

Δ_f H [C₄H₈(g)] = 28.0 kJ/mol; Δ_f H [C(g)] = 715.0 kJ/mol; Δ_f H [H(g)] = 218.0 kJ/mol

BE (C-C) = 348.0 kJ/mol; BE (C-H) = 412.0 kJ/mol.

TestHub · Accepted Answer

Unstrained cyclobutane (4 C–C, 8 C–H): To atomize 4C(s) + 4H₂ (g), the energy required is 4(715) + 8(218) = 4604 kJ. The energy released when bonds are formed is 4(348) + 8(412) = 4688 kJ. Therefore, the enthalpy of formation for unstrained cyclobutane is Δ_f H(unstrained) = 4604 - 4688 = -84 kJ/mol.

The strain energy is calculated as 28 - (-84) = 112 kJ/mol. This corresponds to option (a).

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